Common/Compiler: Introduced XR_ASSUME() macro.

There is the only one "assume" usage yet, but the macro is useful for
future optimization.

Author: Kaffeine

src/Common/Compiler.inl

@@ -14,6 +14,12 @@
 #define XR_IMPORT __declspec(dllimport)
 #endif
 
+#if defined(__GNUC__)
+#define XR_ASSUME(expr)  if (expr){} else __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define XR_ASSUME(expr) __assume(expr)
+#endif
+
 #if defined(__GNUC__)
 #define NO_INLINE __attribute__((noinline))
 #define FORCE_INLINE __attribute__((always_inline)) inline