Fix the build for gcc on os x: gcc warns about the missing return in protcatchthread, but we don't want to add one because that would be unreachable code. so use __attribute__((__noreturn__)) instead.

Copied from Perforce
 Change: 185461
 ServerID: perforce.ravenbrook.com

mps/code/config.h

@@ -231,6 +231,16 @@
 #define ATTRIBUTE_NO_SANITIZE_ADDRESS
 #endif
 
+/* Attribute for functions that do not return.
+ * GCC: <http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html>
+ * Clang: <http://clang.llvm.org/docs/AttributeReference.html#id1>
+ */
+#if defined(MPS_BUILD_GC) || defined(MPS_BUILD_LL)
+#define ATTRIBUTE_NORETURN __attribute__((__noreturn__))
+#else
+#define ATTRIBUTE_NORETURN
+#endif
+
 
 /* EPVMDefaultSubsequentSegSIZE is a default for the alignment of
  * subsequent segments (non-initial at each save level) in EPVM.  See

mps/code/protxc.c

@@ -282,6 +282,7 @@ static void protCatchOne(void)
  * handler won't cause a deadlock.
  */
 
+ATTRIBUTE_NORETURN
 static void *protCatchThread(void *p) {
   UNUSED(p);
   for (;;)