Stop cleaning gem artifacts

Bulk builds have seen occasional failures building
textproc/ruby-commonmarker, which is the only reverse dependency. I'm
not positive the cleaning of gem artifacts is the cause of the failure,
though I suspect it is.

Discussed with naddy@

devel/ruby-rb_sys/Makefile

@@ -3,6 +3,7 @@ COMMENT =	helpers for compiling Rust extensions for Ruby
 DISTNAME =	rb_sys-0.9.85
 CATEGORIES =	devel
 HOMEPAGE =	https://oxidize-rb.github.io/rb-sys/
+REVISION =	0
 
 # Apache/MIT License
 PERMIT_PACKAGE =	Yes

devel/ruby-rb_sys/patches/patch-lib_rb_sys_mkmf_rb

@@ -0,0 +1,15 @@
+Do not clean gem artifacts after build. Doing so can lead to rebuilds
+and failures.
+
+Index: lib/rb_sys/mkmf.rb
+--- lib/rb_sys/mkmf.rb.orig
++++ lib/rb_sys/mkmf.rb
+@@ -139,8 +139,6 @@ module RbSys
+         \t$(INSTALL_PROG) $(DLLIB) $(RUBYARCHDIR)
+ 
+         gemclean:
+-        \t$(ECHO) Cleaning gem artifacts
+-        \t-$(Q)$(RM_RF) $(RUBYGEMS_CLEAN_DIRS) 2> /dev/null || true
+ 
+         install: #{builder.clean_after_install ? "install-so gemclean" : "install-so"}
+