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.

1 files changed, 8 insertions, 5 deletions

diff --git a/Makefile.SH b/Makefile.SH
index c8ad2a8f52..6577cc3e58 100755
--- a/Makefile.SH
+++ b/Makefile.SH
@@ -419,7 +419,7 @@ esac
 ## In the following dollars and backticks do not need the extra backslash.
 $spitshell >>$Makefile <<'!NO!SUBS!'
 
-private = preplibrary $(CONFIGPM) $(CONFIGPOD) lib/ExtUtils/Miniperl.pm git_version.h
+private = preplibrary $(CONFIGPM) $(CONFIGPOD) lib/ExtUtils/Miniperl.pm git_version.h lib/buildcustomize.pl
 
 # Files to be built with variable substitution before miniperl
 # is available.
@@ -999,6 +999,9 @@ lib/re.pm: ext/re/re.pm
 	@-rm -f $@
 	cp ext/re/re.pm lib/re.pm
 
+lib/buildcustomize.pl: $(MINIPERL_EXE) write_buildcustomize.pl
+	$(MINIPERL) write_buildcustomize.pl >lib/buildcustomize.pl
+
 unidatafiles $(unidatafiles) pod/perluniprops.pod: uni.data
 
 uni.data: $(MINIPERL_EXE) $(CONFIGPM) lib/unicore/mktables $(nonxs_ext)
@@ -1167,16 +1170,16 @@ manicheck:	FORCE
 #
 # DynaLoader may be needed for extensions that use Makefile.PL.
 
-$(DYNALOADER):	$(MINIPERL_EXE) preplibrary FORCE $(nonxs_ext)
+$(DYNALOADER):	$(MINIPERL_EXE) lib/buildcustomize.pl preplibrary FORCE $(nonxs_ext)
 	$(MINIPERL) make_ext.pl $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=static $(STATIC_LDFLAGS)
 
-d_dummy $(dynamic_ext):	$(MINIPERL_EXE) preplibrary makeppport $(DYNALOADER) FORCE $(PERLEXPORT)
+d_dummy $(dynamic_ext):	$(MINIPERL_EXE) lib/buildcustomize.pl preplibrary makeppport $(DYNALOADER) FORCE $(PERLEXPORT)
 	$(MINIPERL) make_ext.pl $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=dynamic
 
-s_dummy $(static_ext):	$(MINIPERL_EXE) preplibrary makeppport $(DYNALOADER) FORCE
+s_dummy $(static_ext):	$(MINIPERL_EXE) lib/buildcustomize.pl preplibrary makeppport $(DYNALOADER) FORCE
 	$(MINIPERL) make_ext.pl $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=static $(STATIC_LDFLAGS)
 
-n_dummy $(nonxs_ext):	$(MINIPERL_EXE) preplibrary FORCE
+n_dummy $(nonxs_ext):	$(MINIPERL_EXE) lib/buildcustomize.pl preplibrary FORCE
 	$(MINIPERL) make_ext.pl $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL)
 !NO!SUBS!