Revert "Make mrb_load_exec a static function."

This reverts commit 7944d9a.
Because it voids #3248 and #3331. But we should add better way
to check whether compile errors occur without duplicated callings.

include/mruby/compile.h

@@ -175,6 +175,7 @@ MRB_API struct mrb_parser_state* mrb_parse_file(mrb_state*,FILE*,mrbc_context*);
 MRB_API struct mrb_parser_state* mrb_parse_string(mrb_state*,const char*,mrbc_context*);
 MRB_API struct mrb_parser_state* mrb_parse_nstring(mrb_state*,const char*,int,mrbc_context*);
 MRB_API struct RProc* mrb_generate_code(mrb_state*, struct mrb_parser_state*);
+MRB_API mrb_value mrb_load_exec(mrb_state *mrb, struct mrb_parser_state *p, mrbc_context *c);
 
 /* program load functions */
 #ifndef MRB_DISABLE_STDIO

mrbgems/mruby-compiler/core/parse.y

@@ -5765,7 +5765,7 @@ mrb_parse_string(mrb_state *mrb, const char *s, mrbc_context *c)
   return mrb_parse_nstring(mrb, s, strlen(s), c);
 }
 
-static mrb_value
+MRB_API mrb_value
 mrb_load_exec(mrb_state *mrb, struct mrb_parser_state *p, mrbc_context *c)
 {
   struct RClass *target = mrb->object_class;