common.mk: define MJIT_HEADER earlier

so that other predefined macros won't be removed by
`MJITHeader.remove_predefined_macros!`.

Currently macro like -DVM_CHECK_MODE=2 is removed when it's passed in
configure. But it is needed during JIT compilation.

gc.c: export rb_obj_info to let JIT succeed with VM_CHECK_MODE=2.

```
MJIT warning: failure in loading code from '/tmp/_ruby_mjit_p15631u0.so': /tmp/_ruby_mjit_p15631u0.so: undefined symbol: rb_obj_info
```

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 2 insertions, 2 deletions

diff --git a/common.mk b/common.mk
index 69fc6e42af..0449d24dd5 100644
--- a/common.mk
+++ b/common.mk
@@ -213,7 +213,7 @@ mjit_config.h: Makefile
 
 $(TIMESTAMPDIR)/$(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).time: probes.h vm.$(OBJEXT)
 	$(ECHO) building $(@F:.time=.h)
-	$(Q) $(CPP) $(MJIT_HEADER_FLAGS) $(CFLAGS) $(XCFLAGS) $(CPPFLAGS) -DMJIT_HEADER $(srcdir)/vm.c $(CPPOUTFLAG)$(@F:.time=.h).new
+	$(Q) $(CPP) -DMJIT_HEADER $(MJIT_HEADER_FLAGS) $(CFLAGS) $(XCFLAGS) $(CPPFLAGS) $(srcdir)/vm.c $(CPPOUTFLAG)$(@F:.time=.h).new
 	$(Q) $(IFCHANGE) "--timestamp=$@" $(@F:.time=.h) $(@F:.time=.h).new
 
 $(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).h: $(TIMESTAMPDIR)/$(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).time
diff --git a/gc.c b/gc.c
index be0dd701ff..a1e6bc4bc2 100644
--- a/gc.c
+++ b/gc.c
@@ -9452,7 +9452,7 @@ obj_info(VALUE obj)
 }
 #endif
 
-const char *
+MJIT_FUNC_EXPORTED const char *
 rb_obj_info(VALUE obj)
 {
     if (!rb_special_const_p(obj)) {