[add prototype for gc_alloc
John Meacham <john@repetae.net>**20120220050616
 Ignore-this: 444b34148332459dc0e3d32b7c55d3e0
] hunk ./rts/rts/gc_jgc.h 28
+void *(gc_alloc)(gc_t gc,struct s_cache **sc, unsigned count, unsigned nptrs);