dev-lang/ruby: fix build during bootstrap

Fix building during a bootstrap situation where no ruby is present yet.
Normally ruby uses a pregenerated miniprelude.c file for a miniruby that
is functional enough to assist the build process. Since we now patch
gem_prelude.rb in f6aa0fc2dc the Makefile
tries to regenerate miniprelude.c, but this first requires a working
ruby, leading to build failures.

By resetting the date of the patched gem_prelude.c we can avoid this.
The gem_predule.rb patch is intended to be used in an installed ruby and
does not affect the miniruby usage.

Closes: https://bugs.gentoo.org/787137
Package-Manager: Portage-3.0.18, Repoman-3.0.2
Signed-off-by: Hans de Graaff <graaff@gentoo.org>

dev-lang/ruby/ruby-2.7.3-r1.ebuild

@@ -67,6 +67,10 @@ src_prepare() {
 	# compiles ruby in a non-standard way, may be dropped
 	eapply "${FILESDIR}"/2.7/{002,003,010}*.patch
 
+	# Reset time on patched gem_prelude.rb to avoid the need for a base
+	# ruby during bootstrapping, bug 787137
+	touch -t 202001010000 gem_prelude.rb || die
+
 	einfo "Unbundling gems..."
 	cd "$S"
 	# Remove bundled gems that we will install via PDEPEND, bug