Halt (#372)

* Base: collapse two CPP branches

The two branches are identical and just define the same macro on different
architectures.  Collapse them to simplify.  Yes, Windows is supported on all
those architectures.

* Base: tweak __builtin_unreachable on Windows

Windows could be using a GNU compatible compiler (i.e. clang).  In such a
scenario, assume that __builtin_unreachable() is available (any newer clang or
gcc would suffice).  However, since we require clang for swift, it makes sense
to require clang for Foundation build.  The minimal require clang already has
__builtin_unreachable supported.

On a non-GNU-like compiler, use the MSVC intrinsic `__assume` which gives a
proper `__builtin_unreachable` equivalent.

* Base: spell DebugBreak __builtin_trap

Use another macro to make the two cases more similar.  NFC.

Author: compnerd

CoreFoundation/Base.subproj/CFInternal.h

@@ -158,22 +158,17 @@ CF_PRIVATE CFIndex __CFActiveProcessorCount();
 #endif
 
 #if DEPLOYMENT_TARGET_WINDOWS
-#define __builtin_unreachable() do { } while (0)
+#if !defined(__GNUC__)
+#define __builtin_trap() DebugBreak()
+#define __builtin_unreachable() __assume(0)
+#endif
 #endif
 
-#if defined(__i386__) || defined(__x86_64__)
-    #if defined(__GNUC__)
-        #define HALT do {__builtin_trap(); kill(getpid(), 9); __builtin_unreachable(); } while (0)
-    #elif defined(_MSC_VER)
-        #define HALT do { DebugBreak(); abort(); __builtin_unreachable(); } while (0)
-    #else
-        #error Compiler not supported
-    #endif
-#elif defined(__ppc__) || (__arm__) || (__aarch64__)
+#if defined(__i386__) || defined(__x86_64__) || defined(__ppc__) || (__arm__) || (__aarch64__)
     #if defined(__GNUC__)
         #define HALT do {__builtin_trap(); kill(getpid(), 9); __builtin_unreachable(); } while (0)
     #elif defined(_MSC_VER)
-        #define HALT do { DebugBreak(); abort(); __builtin_unreachable(); } while (0)
+        #define HALT do { __builtin_trap(); abort(); __builtin_unreachable(); } while (0)
     #else
         #error Compiler not supported
     #endif