gc: fix bad c++ casts.

This C++ regression snuck into in Version 286; I didn't
check C++ compilation.

* lib.h (container): Macro must use coerce not
convert because mem_t * isn't void *.

* gc.c (gc_prot_array_alloc): Likewise.

1 files changed, 2 insertions, 2 deletions

diff --git a/lib.h b/lib.h
index dc90aa23..8448db55 100644
--- a/lib.h
+++ b/lib.h
@@ -47,8 +47,8 @@ typedef double_uintptr_t dbl_ucnum;
 #endif
 
 #define container(PTR, TYPE, MEMB)                          \
-  convert(TYPE *,                                           \
-          convert(mem_t *, (PTR)) - offsetof(TYPE, MEMB))
+  coerce(TYPE *,                                            \
+         coerce(mem_t *, (PTR)) - offsetof(TYPE, MEMB))
 
 #if __STDC_VERSION__ >= 199901L
 #define FLEX_ARRAY