Add the QT_HAS_xxx macros for post-C++11 feature testing

And for compiler extensions. QT_HAS_BUILTIN and QT_HAS_ATTRIBUTE will
come in handy.

Change-Id: I255870833a024a36adf6ffff13ecf06624bfc1ef
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/global/qcompilerdetection.h

@@ -1109,6 +1109,37 @@
 #  define Q_DECL_CONST_FUNCTION Q_DECL_PURE_FUNCTION
 #endif
 
+/*
+ * SG10's SD-6 feature detection and some useful extensions from Clang and GCC
+ * https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations
+ * http://clang.llvm.org/docs/LanguageExtensions.html#feature-checking-macros
+ */
+#ifdef __has_builtin
+#  define QT_HAS_BUILTIN(x)             __has_builtin(x)
+#else
+#  define QT_HAS_BUILTIN(x)             0
+#endif
+#ifdef __has_attribute
+#  define QT_HAS_ATTRIBUTE(x)           __has_attribute(x)
+#else
+#  define QT_HAS_ATTRIBUTE(x)           0
+#endif
+#ifdef __has_cpp_attribute
+#  define QT_HAS_CPP_ATTRIBUTE(x)       __has_cpp_attribute(x)
+#else
+#  define QT_HAS_CPP_ATTRIBUTE(x)       0
+#endif
+#ifdef __has_include
+#  define QT_HAS_INCLUDE(x)             __has_include(x)
+#else
+#  define QT_HAS_INCLUDE(x)             0
+#endif
+#ifdef __has_include_next
+#  define QT_HAS_INCLUDE_NEXT(x)        __has_include_next(x)
+#else
+#  define QT_HAS_INCLUDE_NEXT(x)        0
+#endif
+
 /*
  * Warning/diagnostic handling
  */

src/corelib/global/qendian.h

@@ -87,12 +87,6 @@ template <typename T> inline T qFromUnaligned(const uchar *src)
 */
 template <typename T> T qbswap(T source);
 
-#ifdef __has_builtin
-#  define QT_HAS_BUILTIN(x)     __has_builtin(x)
-#else
-#  define QT_HAS_BUILTIN(x)     0
-#endif
-
 // GCC 4.3 implemented all the intrinsics, but the 16-bit one only got implemented in 4.8;
 // Clang 2.6 implemented the 32- and 64-bit but waited until 3.2 to implement the 16-bit one
 #if (defined(Q_CC_GNU) && Q_CC_GNU >= 403) || QT_HAS_BUILTIN(__builtin_bswap32)
@@ -154,8 +148,6 @@ template <> inline quint16 qbswap<quint16>(quint16 source)
 }
 #endif // GCC & Clang intrinsics
 
-#undef QT_HAS_BUILTIN
-
 // signed specializations
 template <> inline qint64 qbswap<qint64>(qint64 source)
 {

src/corelib/global/qlogging.cpp

@@ -75,17 +75,13 @@
 # include "private/qcore_unix_p.h"
 #endif
 
-#ifndef __has_include
-#  define __has_include(x) 0
-#endif
-
 #ifndef QT_BOOTSTRAPPED
 #if !defined QT_NO_REGULAREXPRESSION
 #  ifdef __UCLIBC__
 #    if __UCLIBC_HAS_BACKTRACE__
 #      define QLOGGING_HAVE_BACKTRACE
 #    endif
-#  elif (defined(__GLIBC__) && defined(__GLIBCXX__)) || (__has_include(<cxxabi.h>) && __has_include(<execinfo.h>))
+#  elif (defined(__GLIBC__) && defined(__GLIBCXX__)) || (QT_HAS_INCLUDE(<cxxabi.h>) && QT_HAS_INCLUDE(<execinfo.h>))
 #    define QLOGGING_HAVE_BACKTRACE
 #  endif
 #endif
@@ -94,7 +90,7 @@
 extern char *__progname;
 #endif
 
-#if defined(Q_OS_LINUX) && (defined(__GLIBC__) || __has_include(<sys/syscall.h>))
+#if defined(Q_OS_LINUX) && (defined(__GLIBC__) || QT_HAS_INCLUDE(<sys/syscall.h>))
 #  include <sys/syscall.h>
 static long qt_gettid()
 {

src/corelib/global/qnumeric_p.h

@@ -56,10 +56,6 @@
 #  include <immintrin.h>    // for _addcarry_u<nn>
 #endif
 
-#ifndef __has_builtin
-#  define __has_builtin(x)  0
-#endif
-
 QT_BEGIN_NAMESPACE
 
 #if !defined(Q_CC_MIPS)
@@ -230,28 +226,28 @@ mul_overflow(T v1, T v2, T *r)
 #endif
 
 // GCC 5 and Clang have builtins to detect overflows
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_uadd_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_uadd_overflow)
 template <> inline bool add_overflow(unsigned v1, unsigned v2, unsigned *r)
 { return __builtin_uadd_overflow(v1, v2, r); }
 #endif
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_uaddl_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_uaddl_overflow)
 template <> inline bool add_overflow(unsigned long v1, unsigned long v2, unsigned long *r)
 { return __builtin_uaddl_overflow(v1, v2, r); }
 #endif
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_uaddll_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_uaddll_overflow)
 template <> inline bool add_overflow(unsigned long long v1, unsigned long long v2, unsigned long long *r)
 { return __builtin_uaddll_overflow(v1, v2, r); }
 #endif
 
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_umul_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_umul_overflow)
 template <> inline bool mul_overflow(unsigned v1, unsigned v2, unsigned *r)
 { return __builtin_umul_overflow(v1, v2, r); }
 #endif
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_umull_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_umull_overflow)
 template <> inline bool mul_overflow(unsigned long v1, unsigned long v2, unsigned long *r)
 { return __builtin_umull_overflow(v1, v2, r); }
 #endif
-#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || __has_builtin(__builtin_umulll_overflow)
+#if (defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && Q_CC_GNU >= 500) || QT_HAS_BUILTIN(__builtin_umulll_overflow)
 template <> inline bool mul_overflow(unsigned long long v1, unsigned long long v2, unsigned long long *r)
 { return __builtin_umulll_overflow(v1, v2, r); }
 #  define HAVE_MUL64_OVERFLOW