Compiler.h: add macro GCC_OLDER_THAN()

src/Compiler.h

@@ -31,13 +31,21 @@
 #define GCC_CHECK_VERSION(major, minor) \
 	(defined(__GNUC__) && GCC_VERSION >= GCC_MAKE_VERSION(major, minor, 0))
 
+/**
+ * Are we building with gcc (not clang or any other compiler) and a
+ * version older than the specified one?
+ */
+#define GCC_OLDER_THAN(major, minor) \
+	(defined(__GNUC__) && !defined(__clang__) && \
+	 GCC_VERSION < GCC_MAKE_VERSION(major, minor, 0))
+
 #ifdef __clang__
 #  define CLANG_VERSION GCC_MAKE_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
 #  if __clang_major__ < 3
 #    error Sorry, your clang version is too old.  You need at least version 3.1.
 #  endif
 #elif defined(__GNUC__)
-#  if !GCC_CHECK_VERSION(4,6)
+#  if GCC_OLDER_THAN(4,6)
 #    error Sorry, your gcc version is too old.  You need at least version 4.6.
 #  endif
 #else
@@ -138,7 +146,7 @@
 #if defined(__cplusplus)
 
 /* support for C++11 "override" was added in gcc 4.7 */
-#if !defined(__clang__) && !GCC_CHECK_VERSION(4,7)
+#if GCC_OLDER_THAN(4,7)
 #define override
 #define final
 #endif

src/util/Manual.hxx

@@ -35,7 +35,7 @@
 #include <new>
 #include <utility>
 
-#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
+#if GCC_OLDER_THAN(4,8)
 #include <type_traits>
 #endif
 
@@ -54,7 +54,7 @@
  */
 template<class T>
 class Manual {
-#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
+#if GCC_OLDER_THAN(4,8)
 	/* no alignas() on gcc < 4.8: apply worst-case fallback */
 	__attribute__((aligned(8)))
 #else