tcg/tcg.h: Remove GCC check for tcg_debug_assert() macro

Both GCC v4.8 and Clang v3.4 (our minimum versions) support
__builtin_unreachable(), so we can remove the version check here now.
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NThomas Huth <thuth@redhat.com>

tcg/tcg.h

@@ -230,11 +230,9 @@ typedef uint64_t tcg_insn_unit;
 
 #if defined CONFIG_DEBUG_TCG || defined QEMU_STATIC_ANALYSIS
 # define tcg_debug_assert(X) do { assert(X); } while (0)
-#elif QEMU_GNUC_PREREQ(4, 5)
+#else
 # define tcg_debug_assert(X) \
     do { if (!(X)) { __builtin_unreachable(); } } while (0)
-#else
-# define tcg_debug_assert(X) do { (void)(X); } while (0)
 #endif
 
 typedef struct TCGRelocation {