Makefile: regenerate *.pm on NO_PERL_CPAN_FALLBACKS change

Regenerate the *.pm files in perl/build/* if the
NO_PERL_CPAN_FALLBACKS flag added to the *.pm files in
1aca69c0195 (perl Git::LoadCPAN: emit better errors under
NO_PERL_CPAN_FALLBACKS, 2018-03-03) is changed.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Makefile b/Makefile
index a15f39e..574b255 100644
--- a/Makefile
+++ b/Makefile
@@ -2275,6 +2275,7 @@
 PERL_DEFINES += $(PERLLIB_EXTRA_SQ)
 PERL_DEFINES += $(perllibdir_SQ)
 PERL_DEFINES += $(RUNTIME_PREFIX)
+PERL_DEFINES += $(NO_PERL_CPAN_FALLBACKS)
 
 # Support Perl runtime prefix. In this mode, a different header is installed
 # into Perl scripts.