Makefile: add NO_PERL_CPAN_FALLBACKS knob

We include some perl modules which are not part of the core perl
install, as a convenience.  This allows us to rely on those modules in
our perl-based tools and scripts without requiring users to install the
modules from CPAN or their operating system packages.

Users whose operating system provides these modules and packagers of Git
often don't want to ship or use these bundled modules.  Allow these
users to set NO_PERL_CPAN_FALLBACKS to avoid installing the bundled
modules.

Signed-off-by: Todd Zullinger <[email protected]>
Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: tmzullinger

Makefile

@@ -296,6 +296,12 @@ all::
 #
 # Define NO_PERL if you do not want Perl scripts or libraries at all.
 #
+# Define NO_PERL_CPAN_FALLBACKS if you do not want to install bundled
+# copies of CPAN modules that serve as a fallback in case the modules
+# are not available on the system. This option is intended for
+# distributions that want to use their packaged versions of Perl
+# modules, instead of the fallbacks shipped with Git.
+#
 # Define PYTHON_PATH to the path of your Python binary (often /usr/bin/python
 # but /usr/bin/python2.7 on some platforms).
 #
@@ -2305,8 +2311,10 @@ LIB_CPAN_GEN := $(patsubst perl/%.pm,perl/build/lib/%.pm,$(LIB_CPAN))
 
 ifndef NO_PERL
 all:: $(LIB_PERL_GEN)
+ifndef NO_PERL_CPAN_FALLBACKS
 all:: $(LIB_CPAN_GEN)
 endif
+endif
 
 perl/build/lib/%.pm: perl/%.pm
 	$(QUIET_GEN)mkdir -p $(dir $@) && \