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

1 files changed, 1 insertions, 1 deletions

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)) {