Use more than just "does it claim to be GCC?" to test for attributes.

Not all versions of GCC or Clang have the returns_nonnull function
attribute, so use the same technique used in current master branch
libpcap - use __has_attribute() if it's available, otherwise use
compiler version tests.

This also lets us use WS_NORETURN on some non-GCC compilers.

Change-Id: I6ca4a81797ebfca9f743e16f83839c49d303da81
Reviewed-on: https://code.wireshark.org/review/24083
Reviewed-by: Guy Harris <guy@alum.mit.edu>

ws_attributes.h

@@ -35,6 +35,119 @@ extern "C" {
  * XXX - similar hints for other compilers?
  */
 
+/*
+ * This was introduced by Clang:
+ *
+ *     http://clang.llvm.org/docs/LanguageExtensions.html#has-attribute
+ *
+ * in some version (which version?); it has been picked up by GCC 5.0.
+ */
+#ifndef __has_attribute
+  /*
+   * It's a macro, so you can check whether it's defined to check
+   * whether it's supported.
+   *
+   * If it's not, define it to always return 0, so that we move on to
+   * the fallback checks.
+   */
+  #define __has_attribute(x) 0
+#endif
+
+/*
+ * Note that the C90 spec's "6.8.1 Conditional inclusion" and the
+ * C99 spec's and C11 spec's "6.10.1 Conditional inclusion" say:
+ *
+ *    Prior to evaluation, macro invocations in the list of preprocessing
+ *    tokens that will become the controlling constant expression are
+ *    replaced (except for those macro names modified by the defined unary
+ *    operator), just as in normal text.  If the token "defined" is
+ *    generated as a result of this replacement process or use of the
+ *    "defined" unary operator does not match one of the two specified
+ *    forms prior to macro replacement, the behavior is undefined.
+ *
+ * so you shouldn't use defined() in a #define that's used in #if or
+ * #elif.  Some versions of Clang, for example, will warn about this.
+ *
+ * Instead, we check whether the pre-defined macros for particular
+ * compilers are defined and, if not, define the "is this version XXX
+ * or a later version of this compiler" macros as 0.
+ */
+
+/*
+ * Check whether this is GCC major.minor or a later release, or some
+ * compiler that claims to be "just like GCC" of that version or a
+ * later release.
+ */
+
+#if !defined(__GNUC__)
+  #define WS_IS_AT_LEAST_GNUC_VERSION(major, minor) 0
+#else
+  #define WS_IS_AT_LEAST_GNUC_VERSION(major, minor) \
+	(__GNUC__ > (major) || \
+	 (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
+#endif
+
+/*
+ * Check whether this is Sun C/SunPro C/Oracle Studio major.minor
+ * or a later release.
+ *
+ * The version number in __SUNPRO_C is encoded in hex BCD, with the
+ * uppermost hex digit being the major version number, the next
+ * one or two hex digits being the minor version number, and
+ * the last digit being the patch version.
+ *
+ * It represents the *compiler* version, not the product version;
+ * see
+ *
+ *    https://sourceforge.net/p/predef/wiki/Compilers/
+ *
+ * for a partial mapping, which we assume continues for later
+ * 12.x product releases.
+ */
+
+#if !defined(__SUNPRO_C)
+  #define WS_IS_AT_LEAST_SUNC_VERSION(major,minor) 0
+#else
+  #define WS_SUNPRO_VERSION_TO_BCD(major, minor) \
+	(((minor) >= 10) ? \
+	    (((major) << 12) | (((minor)/10) << 8) | (((minor)%10) << 4)) : \
+	    (((major) << 8) | ((minor) << 4)))
+  #define WS_IS_AT_LEAST_SUNC_VERSION(major,minor) \
+	(__SUNPRO_C >= WS_SUNPRO_VERSION_TO_BCD((major), (minor)))
+#endif
+
+/*
+ * Check whether this is IBM XL C major.minor or a later release.
+ *
+ * The version number in __xlC__ has the major version in the
+ * upper 8 bits and the minor version in the lower 8 bits.
+ */
+
+#if !defined(__xlC__)
+  #define WS_IS_AT_LEAST_XL_C_VERSION(major,minor) 0
+#else
+  #define WS_IS_AT_LEAST_XL_C_VERSION(major, minor) \
+	(__xlC__ >= (((major) << 8) | (minor)))
+#endif
+
+/*
+ * Check whether this is HP aC++/HP C major.minor or a later release.
+ *
+ * The version number in __HP_aCC is encoded in zero-padded decimal BCD,
+ * with the "A." stripped off, the uppermost two decimal digits being
+ * the major version number, the next two decimal digits being the minor
+ * version number, and the last two decimal digits being the patch version.
+ * (Strip off the A., remove the . between the major and minor version
+ * number, and add two digits of patch.)
+ */
+
+#if !defined(__HP_aCC)
+  #define WS_IS_AT_LEAST_HP_C_VERSION(major,minor) 0
+#else
+  #define WS_IS_AT_LEAST_HP_C_VERSION(major,minor) \
+	(__HP_aCC >= ((major)*10000 + (minor)*100))
+#endif
+
 #if defined(__GNUC__)
   /* This includes clang */
   #define _U_ __attribute__((unused))
@@ -42,19 +155,36 @@ extern "C" {
   #define _U_
 #endif
 
-/* Hint to the compiler that a function never returns */
-#if defined(__GNUC__)
-  /* This includes clang */
+/*
+ * WS_NORETURN, before a function declaration, means "this function
+ * never returns".  (It must go before the function declaration, e.g.
+ * "extern WS_NORETURN func(...)" rather than after the function
+ * declaration, as the MSVC version has to go before the declaration.)
+ */
+#if __has_attribute(noreturn) \
+    || WS_IS_AT_LEAST_GNUC_VERSION(2,5) \
+    || WS_IS_AT_LEAST_SUNC_VERSION(5,9) \
+    || WS_IS_AT_LEAST_XL_C_VERSION(10,1) \
+    || WS_IS_AT_LEAST_HP_C_VERSION(6,10)
+  /*
+   * Compiler with support for __attribute__((noreturn)), or GCC 2.5 and
+   * later, or Solaris Studio 12 (Sun C 5.9) and later, or IBM XL C 10.1
+   * and later (do any earlier versions of XL C support this?), or
+   * HP aCC A.06.10 and later.
+   */
   #define WS_NORETURN __attribute__((noreturn))
 #elif defined(_MSC_VER)
+  /*
+   * MSVC.
+   */
   #define WS_NORETURN __declspec(noreturn)
 #else
   #define WS_NORETURN
 #endif
 
 /* Hint to the compiler that the function returns a non-null value */
-#if defined(__GNUC__)
-  /* This includes clang */
+#if __has_attribute(returns_nonnull) \
+    || WS_IS_AT_LEAST_GNUC_VERSION(4,9)
   #define WS_RETNONNULL __attribute__((returns_nonnull))
 #else
   #define WS_RETNONNULL