gc: c++ fix in type_t conversion.

* gc.c (sweep_one): The recent fix to address the clang
diagnostic from -fsanitize=implicit-conversion broke C++
compatibility, due to enums being type safe. We revert the
expression to the original, before that fix, and address the
clang diagnostic differently.

* gc.h (REACHABLE, FREE): Add a U suffix to the constants to
make them unsigned.  The implicit conversion issue in the
expression convert(type_t, block->t.type & ~REACHABLE)
is that ~REACHABLE is -257, and is being converted to
unsigned.

2 files changed, 3 insertions, 3 deletions

diff --git a/gc.c b/gc.c
index 311f66d2..0c727ed4 100644
--- a/gc.c
+++ b/gc.c
@@ -606,7 +606,7 @@ static int sweep_one(obj_t *block)
 #if CONFIG_GEN_GC
     block->t.gen = 1;
 #endif
-    block->t.type &= convert(type_t, ~REACHABLE);
+    block->t.type = convert(type_t, block->t.type & ~REACHABLE);
     return 0;
   }
 
diff --git a/gc.h b/gc.h
index 6103781a..a575ec88 100644
--- a/gc.h
+++ b/gc.h
@@ -66,8 +66,8 @@ extern val break_obj;
 #endif
 
 #define gc_hint(var) gc_hint_func(&var)
-#define REACHABLE 0x100
-#define FREE      0x200
+#define REACHABLE 0x100U
+#define FREE      0x200U
 
 INLINE val zap(volatile val *loc) { val ret = *loc; *loc = nil; return ret; }