tools include: Adopt __compiletime_error

From the kernel, get the gcc one and provide the fallback so that we can
continue build with other compilers, such as with clang.

Will be used by tools/arch/x86/include/asm/cmpxchg.h.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-pecgz6efai4a9euuk4rxuotr@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/include/linux/compiler-gcc.h

@@ -12,3 +12,7 @@
 #if GCC_VERSION >= 70000 && !defined(__CHECKER__)
 # define __fallthrough __attribute__ ((fallthrough))
 #endif
+
+#if GCC_VERSION >= 40300
+# define __compiletime_error(message) __attribute__((error(message)))
+#endif /* GCC_VERSION >= 40300 */

tools/include/linux/compiler.h

@@ -5,6 +5,10 @@
 #include <linux/compiler-gcc.h>
 #endif
 
+#ifndef __compiletime_error
+# define __compiletime_error(message)
+#endif
+
 /* Optimization barrier */
 /* The "volatile" is due to gcc bugs */
 #define barrier() __asm__ __volatile__("": : :"memory")