compiler.h: Use glue() in QEMU_BUILD_BUG_ON define

Rather than rolling custom concatenate-strings macros for the
QEMU_BUILD_BUG_ON macro to use, use the glue() macro we already
have (since it's now available to us in this header).
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NDaniel P. Berrange <berrange@redhat.com>

include/qemu/compiler.h

@@ -89,10 +89,8 @@
 #define inline always_inline
 #endif
 
-#define cat(x,y) x ## y
-#define cat2(x,y) cat(x,y)
 #define QEMU_BUILD_BUG_ON(x) \
-    typedef char cat2(qemu_build_bug_on__,__LINE__)[(x)?-1:1] __attribute__((unused));
+    typedef char glue(qemu_build_bug_on__,__LINE__)[(x)?-1:1] __attribute__((unused));
 
 #if defined __GNUC__
 # if !QEMU_GNUC_PREREQ(4, 4)