nasmlib.h: Introduce nasm_build_assert

It's useful to protect our self from some
errors at build time.

For this sake we should use nasm_build_assert
if needed.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

nasmlib.h

@@ -172,6 +172,11 @@ no_return nasm_assert_failed(const char *, int, const char *);
             nasm_assert_failed(__FILE__,__LINE__,#x);           \
     } while (0)
 
+/*
+ * NASM failure at build time if x != 0
+ */
+#define nasm_build_assert(x) (void)(sizeof(char[1-2*!!(x)]))
+
 /*
  * ANSI doesn't guarantee the presence of `stricmp' or
  * `strcasecmp'.