Use a buildcustomize.pl to set @INC in miniperl when building extensions.

With the build tools now shipped in various subdirectories of cpan/ and dist/
we need to add several paths to @INC when invoking MakeMaker (etc) to build
extensions.

The previous approach of using $ENV{PERL5LIB} was fragile, because:
a: It was hitting the length limit for %ENV variables on VMS
b: It was running the risk of race conditions in a parallel build -
   ExtUtils::Makemaker "knows" to add -I../..lib, which puts lib at the *front*
   of @INC, but if one parallel process happens to copy a module into lib/
   whilst another is searching for it, the second may get a partial read
c: Overwriting $ENV{PERL5LIB} breaks any system where any of the installed
   build tools are actually implemented in Perl, if they are relying on
   $ENV{PERL5LIB} for setup

This approach

a: Doesn't have %ENV length limits
b: Ensures that lib/ is last, so copy targets are always shadowing copy
   sources
c: Only affects miniperl, and doesn't touch $ENV{PERL5LIB}

Approaches that turned out to have fatal flaws:

1: Using $ENV{PERL5OPT} with a module fails because ExtUtils::MakeMaker
   searches for the build perl without setting lib, and treats the error
   caused by a failed -M as "not a valid perl 5 binary"
2: Refactoring ExtUtils::MakeMaker to *not* use -I for lib, and instead rely
   on $ENV{PERL5LIB} [which includes "../../lib"] fails because:
   some extensions have subdirectories, and on these EU::MM correctly uses
   -I../../../lib, where as $ENV{PERL5LIB} only has space for relative paths,
   and only with two levels.

This approach actually takes advantage of ExtUtils::MakeMaker setting an -I
option correct for the depth of directory being built.

2 files changed, 19 insertions, 10 deletions

diff --git a/win32/Makefile b/win32/Makefile
index ceaaaa5ca4..4897a4ad35 100644
--- a/win32/Makefile
+++ b/win32/Makefile
@@ -858,6 +858,9 @@ $(CONFIGPM) : $(MINIPERL) ..\config.sh config_h.PL ..\minimod.pl
 	-$(MINIPERL) -I..\lib $(ICWD) config_h.PL "INST_VER=$(INST_VER)"
 	if errorlevel 1 $(MAKE) /$(MAKEFLAGS) $(CONFIGPM)
 
+..\lib\buildcustomize.pl: $(MINIPERL) ..\write_buildcustomize.pl
+	$(MINIPERL) -I..\lib ..\write_buildcustomize.pl .. >..\lib\buildcustomize.pl
+
 $(MINIPERL) : $(MINIDIR) $(MINI_OBJ)
 	$(LINK32) -subsystem:console -out:$@ @<<
 	$(LINK_FLAGS) $(LIBFILES) $(MINI_OBJ)
@@ -982,24 +985,24 @@ MakePPPort: $(MINIPERL) $(CONFIGPM) Extensions_nonxs
 #-------------------------------------------------------------------------------
 # There's no direct way to mark a dependency on
 # DynaLoader.pm, so this will have to do
-Extensions: ..\make_ext.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
+Extensions: ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --dynamic
 
-Extensions_reonly: ..\make_ext.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
+Extensions_reonly: ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --dynamic +re
 
-Extensions_static : ..\make_ext.pl list_static_libs.pl $(PERLDEP) $(CONFIGPM)
+Extensions_static : ..\make_ext.pl ..\lib\buildcustomize.pl list_static_libs.pl $(PERLDEP) $(CONFIGPM)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --static
 	$(MINIPERL) -I..\lib list_static_libs.pl > Extensions_static
 
-Extensions_nonxs: ..\make_ext.pl $(PERLDEP) $(CONFIGPM)
+Extensions_nonxs: ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --nonxs
 
-$(DYNALOADER) : ..\make_ext.pl $(PERLDEP) $(CONFIGPM) Extensions_nonxs
+$(DYNALOADER) : ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) Extensions_nonxs
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(EXTDIR) --dynaloader
 
@@ -1094,6 +1097,7 @@ distclean: realclean
 	-del /f $(LIBDIR)\Win32CORE.pm
 	-del /f $(LIBDIR)\Win32API\File.pm
 	-del /f $(LIBDIR)\Win32API\File\cFile.pc
+	-del /f $(LIBDIR)\buildcustomize.pl
 	-del /f $(DISTDIR)\XSLoader\XSLoader.pm
 	-if exist $(LIBDIR)\App rmdir /s /q $(LIBDIR)\App
 	-if exist $(LIBDIR)\Archive rmdir /s /q $(LIBDIR)\Archive
diff --git a/win32/makefile.mk b/win32/makefile.mk
index f3fface05a..fcc30ac473 100644
--- a/win32/makefile.mk
+++ b/win32/makefile.mk
@@ -1160,6 +1160,10 @@ $(CONFIGPM) : $(MINIPERL) ..\config.sh config_h.PL ..\minimod.pl
 	$(MINIPERL) -I..\lib $(ICWD) config_h.PL "INST_VER=$(INST_VER)" \
 	    || $(MAKE) $(MAKEMACROS) $(CONFIGPM) $(MAKEFILE)
 
+..\lib\buildcustomize.pl: $(MINIPERL) ..\write_buildcustomize.pl
+	$(MINIPERL) -I..\lib ..\write_buildcustomize.pl .. >..\lib\buildcustomize.pl
+
+
 $(MINIPERL) : $(MINIDIR) $(MINI_OBJ) $(CRTIPMLIBS)
 .IF "$(CCTYPE)" == "BORLAND"
 	if not exist $(CCLIBDIR)\PSDK\odbccp32.lib \
@@ -1370,24 +1374,24 @@ MakePPPort: $(MINIPERL) $(CONFIGPM) Extensions_nonxs
 #-------------------------------------------------------------------------------
 # There's no direct way to mark a dependency on
 # DynaLoader.pm, so this will have to do
-Extensions : ..\make_ext.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
+Extensions : ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --dynamic
 
-Extensions_reonly : ..\make_ext.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
+Extensions_reonly : ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) $(DYNALOADER)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --dynamic +re
 
-Extensions_static : ..\make_ext.pl list_static_libs.pl $(PERLDEP) $(CONFIGPM)
+Extensions_static : ..\make_ext.pl ..\lib\buildcustomize.pl list_static_libs.pl $(PERLDEP) $(CONFIGPM)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --static
 	$(MINIPERL) -I..\lib list_static_libs.pl > Extensions_static
 
-Extensions_nonxs : ..\make_ext.pl $(PERLDEP) $(CONFIGPM)
+Extensions_nonxs : ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM)
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(CPANDIR) --dir=$(DISTDIR) --dir=$(EXTDIR) --nonxs
 
-$(DYNALOADER) : ..\make_ext.pl $(PERLDEP) $(CONFIGPM) Extensions_nonxs
+$(DYNALOADER) : ..\make_ext.pl ..\lib\buildcustomize.pl $(PERLDEP) $(CONFIGPM) Extensions_nonxs
 	$(XCOPY) ..\*.h $(COREDIR)\*.*
 	$(MINIPERL) -I..\lib ..\make_ext.pl "MAKE=$(MAKE)" --dir=$(EXTDIR) --dynaloader
 
@@ -1479,6 +1483,7 @@ distclean: realclean
 	-del /f $(LIBDIR)\Win32CORE.pm
 	-del /f $(LIBDIR)\Win32API\File.pm
 	-del /f $(LIBDIR)\Win32API\File\cFile.pc
+	-del /f $(LIBDIR)\buildcustomize.pl
 	-del /f $(DISTDIR)\XSLoader\XSLoader.pm
 	-if exist $(LIBDIR)\App rmdir /s /q $(LIBDIR)\App
 	-if exist $(LIBDIR)\Archive rmdir /s /q $(LIBDIR)\Archive