Split modular-gc into build and installation

Merged: https://github.com/ruby/ruby/pull/12428

.github/workflows/modgc.yml

@@ -132,7 +132,7 @@ jobs:
       - name: Build Modular  GC
         run: |
           echo "RUBY_GC_LIBRARY=${{ matrix.gc.name }}" >> $GITHUB_ENV
-          make modular-gc MODULAR_GC=${{ matrix.gc.name }} MMTK_BUILD=${{ matrix.gc.mmtk_build }}
+          make install-modular-gc MODULAR_GC=${{ matrix.gc.name }} MMTK_BUILD=${{ matrix.gc.mmtk_build }}
           make distclean-modular-gc MODULAR_GC=${{ matrix.gc.name }}
 
       - run: |

common.mk

@@ -1941,9 +1941,18 @@ rewindable:
 
 HELP_EXTRA_TASKS = ""
 
+gc/Makefile:
+	$(MAKEDIRS) $(@D)
+	$(MESSAGE_BEGIN) \
+	"all:" \
+	"	@echo You must specify MODULAR_GC with the GC to build" \
+	"	@exit 1" \
+	$(MESSAGE_END) > $@
+gc/distclean gc/realclean::
+	-$(Q) $(RM) gc/Makefile
+
 modular-gc-precheck:
-modular-gc: probes.h modular-gc-precheck
-	$(Q) $(MAKEDIRS) $(modular_gc_dir)
+modular-gc: probes.h gc/Makefile
 	$(Q) $(RUNRUBY) $(srcdir)/ext/extmk.rb \
 		$(SCRIPT_ARGS) \
 		--make='$(MAKE)' --make-flags="V=$(V) MINIRUBY='$(MINIRUBY)'" \
@@ -1951,6 +1960,8 @@ modular-gc: probes.h modular-gc-precheck
 		--ext-build-dir=gc --command-output=gc/$(MODULAR_GC)/exts.mk -- \
 		configure gc/$(MODULAR_GC)
 	$(CHDIR) gc/$(MODULAR_GC) && $(exec) $(MAKE) TARGET_SO_DIR=./
+install-modular-gc: modular-gc modular-gc-precheck
+	$(Q) $(MAKEDIRS) $(modular_gc_dir)
 	$(CP) gc/$(MODULAR_GC)/librubygc.$(MODULAR_GC).$(DLEXT) $(modular_gc_dir)
 
 clean-modular-gc: gc/clean

template/Makefile.in

@@ -353,10 +353,6 @@ modular-gc-precheck:
 	    echo "You must configure with --with-modular-gc to use modular GC"; \
 	    exit 1; \
 	fi
-	$(Q) if test -z $(MODULAR_GC); then \
-	    echo "You must specify MODULAR_GC with the GC to build"; \
-	    exit 1; \
-	fi
 
 pre-install-local:: pkgconfig-data