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.

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.

* tests/scripts/options/dash-f: 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.

This reverts commit 6264deece3bb77798240a906ceed79097adbcf48.
Further investigation discovers that the real issue is that
GNU Emacs compile mode doesn't have a matching regex for GNU
make error messages generated when targets fail.  I submitted
a patch to GNU Emacs adding a matcher for compile mode.

Ensure we properly reduce job_slots_used if a command fails because
it doesn't exist/can't be started.

* src/job.h (struct child): Add a field jobslot to be set when using
a job slot.
* src/job.c (start_waiting_job): Remember if we are using a job slot.
(reap_children): Reduce number of job slots used by jobslot.

* tests/scripts/features/errors: Check errors "running" a directory.

* tests/test_driver.pl: Determine non-executable error message.
* tests/scripts/features/errors: Use the local non-executable error.

* src/function.c (func_shell_base): Use error() instead of recreating
the error output.
* src/job.c (exec_command): Show more standard error messages.
* src/load.c (unload_file): Fix whitespace in the error message.
* tests/scripts/features/errors: Add tests for starting non-
existent commands and new error message formats.
* tests/scripts/features/output-sync: New error message formats.
* tests/scripts/functions/shell: Ditto.

Ensure Emacs compile-mode's next-error doesn't match target failure
messages.  Syntax errors in makefiles are still matched.