Avoid cross-contamination between test files by creating a new
working directory for each file, and setting it as the current
directory before starting the tests in that file.

Rename the test output as tNNN.{base,log,diff,mk} where NNN is
a test number starting with 001 for the first test.  It is
slightly more annoying to find diff files since you can't use
autocomplete directly but it is simpler to match things.

Detect the source directory as the location of the test_driver.pl
script, so remove the separate -srcdir option.

* Makefile.am: Remove hacks to create symlinks when building
out-of-tree, and remove -srcdir option from run_make_tests.
* tests/test_driver.pl: Locate $srcpath based on __FILE__, then
compute $toppath as its parent.  Set $scriptpath under $srcpath
and $workpath under the current directory.  Toss $*_filename
and modify get_logfile() etc. to use the suffix directly.  Add
a chdir() around the invocation of the test.
* tests/run_make_tests.pl: Throw out the -srcdir option and use
$srcpath set in test_driver.pl.  The #WORK# helper is no longer
useful so remove it.  Set #PWD# to the current working dir. Always
search the local directory and $srcpath for config-flags.pm.
Use $srcpath for finding the thelp.pl script.
* tests/scripts/features/vpath: Don't put things in work/ as it
is no longer a subdirectory.
* tests/scripts/features/vpathgpath: Ditto.
* tests/scripts/features/vpathplus: Ditto.
* tests/scripts/misc/general1: Ditto.
* tests/scripts/misc/general2: Ditto.
* tests/scripts/options/dash-k: Ditto.
* tests/scripts/options/symlinks: Use $testpath as the working
directory.
* tests/scripts/variables/GNUMAKEFLAGS: Use the test helper to
display env var values (grepping for GNUMAKEFLAGS finds extra things
now that it is our current working directory).

Strawberry Perl has some different behaviors from ActiveState Perl
which impact the test suite:

- Avoid Perl's chomp() as it may not remove CRs; chomp() may remove
  only the final NL but not the CR in a CRNL line ending.
- Strawberry Perl doesn't support ActiveState's system(1, ...) form.
- Strawberry Perl (or msys?) does something weird with "/tmp" when
  provided to exec(), replacing it with the user's %TEMP%.
- Strawberry Perl uses msys paths like /c/foo instead of C:\foo.

* tests/test_driver.pl (get_osname): Strawberry Perl uses 'msys' as
its $^O so if we see that use a port of 'W32'.
(_run_with_timeout): Strawberry Perl doesn't support the special
system(1, ...) form of system() so use POSIX standard fork/exec.
(compare_answer): Paths generated by Strawberry Perl use msys path
format (e.g., /c/foo instead of C:\foo); check for those differences
and compare RE against both the unmodified and modified log.
* tests/run_make_tests.pl (set_defaults): Switch from chomp to s///
to remove CRNL and NL line endings.
* tests/scripts/features/errors: Executing directories on Strawberry
will give an error; translate it to Windows error output format.
* tests/scripts/features/output-sync: Ditto.
* tests/scripts/features/temp_stdin: Ditto.
* tests/scripts/functions/realpath: Ditto.
* tests/scripts/options/dash-I: Ditto.
* tests/scripts/variables/INCLUDE_DIRS: Ditto.
* tests/scripts/misc/close_stdout: /dev/full is reported as existing
on Strawberry Perl, but it doesn't do anything.  Skip the test.
* tests/scripts/variables/MAKEFLAGS: When an argument containing
/tmp is passed to a program via exec(), something replaces it with
the expansion of the %TEMP% variable.  Instead of using /tmp create
a local directory to use.

* src/read.c (eval): If "missing separator" appears to be due to
missing space after ifeq/ifneq, give a hint about the error.
* tests/scripts/misc/failure: Check for these types of failures.
* tests/scripts/variables/special: Move error checking unrelated
to special variables, to misc/failure.

The GNU platform testers reported a number of test errors on
different systems; try to address them.

* tests/thelp.pl: A number of tests timed out with a 4-second
timeout.  Increase the default timeout to 10 seconds.
* tests/run_make_tests.pl: Executing directories on cygwin behaves
differently in Perl than make so skip these tests there.
* tests/scripts/options/symlinks: Check for the symlink feature
in make, rather than whether the system supports them.
* tests/scripts/features/implicit_search: On some systems "false"
exits with a different exit code.  Use the helper instead.
* tests/scripts/features/loadapi: Ditto.
* tests/scripts/features/output-sync: Sleep before make -f bar in
the first test as well as the second one.
* tests/scripts/features/exec: Skip on cygwin, which seems to
be "UNIX" but where scripts don't run normally.
* tests/scripts/misc/fopen-fail: Skip on cygwin, where make
eventually exits with exit code 0 and no error messages.

We already use undef makefile strings to mean "re-use the previous
makefile", so if the string is empty we'll assume it means "don't
use a makefile at all" (don't add -f).

* tests/run_make_tests.pl (run_make_test): If the makefile string
is empty, don't create a makefile or add -f.
* tests/scripts/features/include: Change empty makefile to "\n".
* tests/scripts/misc/close_stdout: Ditto.
* tests/scripts/options/dash-r: Ditto.

* tests/scripts/features/errors: Match Windows-specific errors.
* tests/scripts/features/targetvars: Match Windows-specific errors.
* tests/scripts/misc/general4: Match Windows-specific errors.

GNU make must recognize some special targets as they are defined.
Because of the way targets are defined, we were not recognizing these
special targets until we were handling the NEXT statement.  However
that's too late for some special targets such as .POSIX etc. which can
change the behavior of make during parsing.

Check for special targets earlier, as soon as we've finished parsing
the target introduction line (before we've even parsed the recipe).

* NEWS: Mention the change.
* src/read.c (check_specials): New function to look for special
targets.  Move checks from eval() and record_files() to this new
function.
(eval): Call check_specials() after we've completed parsing the target
introduction line.  Move default goal detection to check_specials().
(record_files): Move handling of .POSIX, .SECONDEXPANSION, and
.ONESHELL to check_specials().
* tests/scripts/misc/bs-nl: Remove workaround for late .POSIX issue.
* tests/scripts/targets/POSIX: Add a comment.

When using execvp() if $PATH is not present in the environment
it will automatically search the system default PATH string.  Emulate
this by passing the system default PATH to find_in_given_path() if
we don't find PATH in the environment.

* src/job.c (child_execute_job): Use confstr(_CS_PATH) if PATH is not
found.

Rather than having an %extraENV that is added to the default %ENV
and resetting %ENV _before_ each test, allow the test setup to
modify %ENV directly as needed then reset %ENV _after_ each test.

* tests/test_driver.pl: Remove unused %extraENV.
(resetENV): Don't add in %extraENV.
(_run_command): Reset after we run the command rather than before.
* tests/scripts/features/export: Convert %extraENV to %ENV
* tests/scripts/features/jobserver: Ditto
* tests/scripts/features/parallelism: Ditto
* tests/scripts/features/targetvars: Ditto
* tests/scripts/functions/eval: Ditto
* tests/scripts/functions/foreach: Ditto
* tests/scripts/functions/origin: Ditto
* tests/scripts/misc/general4: Ditto
* tests/scripts/options/dash-e: Ditto
* tests/scripts/targets/POSIX: Ditto
* tests/scripts/variables/GNUMAKEFLAGS: Ditto
* tests/scripts/variables/SHELL: Ditto