[PATCH:x11proto] Use clang's __has_attribute to check for attribute support

[Alan Coopersmith]

Hopefully other compilers will start adopting this so we don't have to
maintain ever growing matrixes of compiler/version checks for all the
attributes we use.

Signed-off-by: Alan Coopersmith <alan.coopersmith at oracle.com>
---
 Xfuncproto.h.in |   30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/Xfuncproto.h.in b/Xfuncproto.h.in
index 608728f..e9e5e71 100644
--- a/Xfuncproto.h.in
+++ b/Xfuncproto.h.in
@@ -75,15 +75,21 @@ in this Software without prior written authorization from The Open Group.
 #endif
 #endif /* _XFUNCPROTOBEGIN */
 
+/* http://clang.llvm.org/docs/LanguageExtensions.html#has-attribute */
+#ifndef __has_attribute
+# define __has_attribute(x) 0  /* Compatibility with non-clang compilers. */
+#endif
+
 /* Added in X11R6.9, so available in any version of modular xproto */
-#if defined(__GNUC__) && (__GNUC__ >= 4)
+#if __has_attribute(__sentinel__) || (defined(__GNUC__) && (__GNUC__ >= 4))
 # define _X_SENTINEL(x) __attribute__ ((__sentinel__(x)))
 #else
 # define _X_SENTINEL(x)
 #endif /* GNUC >= 4 */
 
 /* Added in X11R6.9, so available in any version of modular xproto */
-#if defined(__GNUC__) && (__GNUC__ >= 4) && !defined(__CYGWIN__) && !defined(__MINGW32__)
+#if (__has_attribute(visibility) || (defined(__GNUC__) && (__GNUC__ >= 4))) \
+    && !defined(__CYGWIN__) && !defined(__MINGW32__)
 # define _X_EXPORT      __attribute__((visibility("default")))
 # define _X_HIDDEN      __attribute__((visibility("hidden")))
 # define _X_INTERNAL    __attribute__((visibility("internal")))
@@ -109,14 +115,16 @@ in this Software without prior written authorization from The Open Group.
 
 /* Bulk branch prediction hints via marking error path functions as "cold" */
 /* requires xproto >= 7.0.25 */
-#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 403) /* 4.3+ */
+#if __has_attribute(__cold__) || \
+    (defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 403)) /* 4.3+ */
 # define _X_COLD __attribute__((__cold__))
 #else
 # define _X_COLD /* nothing */
 #endif
 
 /* Added in X11R6.9, so available in any version of modular xproto */
-#if (defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 301)) \
+#if __has_attribute(deprecated) \
+    || (defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 301)) \
     || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5130))
 # define _X_DEPRECATED  __attribute__((deprecated))
 #else /* not gcc >= 3.1 */
@@ -124,15 +132,17 @@ in this Software without prior written authorization from The Open Group.
 #endif
 
 /* requires xproto >= 7.0.17 */
-#if (defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 205)) \
-	|| (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x590))
+#if __has_attribute(noreturn) \
+    || (defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 205)) \
+    || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x590))
 # define _X_NORETURN __attribute((noreturn))
 #else
 # define _X_NORETURN
 #endif /* GNUC  */
 
 /* Added in X11R6.9, so available in any version of modular xproto */
-#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 203)
+#if __has_attribute(__format__) \
+    || defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 203)
 # define _X_ATTRIBUTE_PRINTF(x,y) __attribute__((__format__(__printf__,x,y)))
 #else /* not gcc >= 2.3 */
 # define _X_ATTRIBUTE_PRINTF(x,y)
@@ -141,14 +151,16 @@ in this Software without prior written authorization from The Open Group.
 /* requires xproto >= 7.0.22 - since this uses either gcc or C99 variable
    argument macros, must be only used inside #ifdef _X_NONNULL guards, as
    many legacy X clients are compiled in C89 mode still. */
-#if defined(__GNUC__) &&  ((__GNUC__ * 100 + __GNUC_MINOR__) >= 303)
+#if __has_attribute(nonnull) \
+    || defined(__GNUC__) &&  ((__GNUC__ * 100 + __GNUC_MINOR__) >= 303)
 #define _X_NONNULL(args...)  __attribute__((nonnull(args)))
 #elif defined(__STDC_VERSION__) && (__STDC_VERSION__ - 0 >= 199901L) /* C99 */
 #define _X_NONNULL(...)  /* */
 #endif
 
 /* requires xproto >= 7.0.22 */
-#if defined(__GNUC__) &&  ((__GNUC__ * 100 + __GNUC_MINOR__) >= 205)
+#if __has_attribute(__unused__) \
+    || defined(__GNUC__) &&  ((__GNUC__ * 100 + __GNUC_MINOR__) >= 205)
 #define _X_UNUSED  __attribute__((__unused__))
 #else
 #define _X_UNUSED  /* */
-- 
1.7.9.2