qfloat16: suppress warning caused by Clang macro we used

Clang implements the _cvtss_sh intrinsic by way of a macro, which
uses a C99 extension and that's not allowed in C++ mode:

 float16.h:119:11: error: compound literals are a C99-specific feature [-Werror,-Wc99-extensions]
 /usr/bin/../lib64/clang/3.9.1/include/f16cintrin.h:76:55: note: expanded from macro '_cvtss_sh'

Reported at https://bugs.llvm.org/show_bug.cgi?id=32491.

Change-Id: I27b55fdf514247549455fffd14b170df75dd4e1f
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/corelib/global/qfloat16.h

@@ -113,6 +113,8 @@ inline Q_REQUIRED_RESULT bool qIsNull(qfloat16 f) Q_DECL_NOTHROW
 inline int qIntCast(qfloat16 f) Q_DECL_NOTHROW
 { return int(static_cast<float>(f)); }
 
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_CLANG("-Wc99-extensions")
 inline qfloat16::qfloat16(float f) Q_DECL_NOTHROW
 {
 #if defined(QT_COMPILER_SUPPORTS_F16C) && defined(__F16C__)
@@ -127,6 +129,7 @@ inline qfloat16::qfloat16(float f) Q_DECL_NOTHROW
           + ((u & 0x007fffff) >> shifttable[(u >> 23) & 0x1ff]);
 #endif
 }
+QT_WARNING_POP
 
 inline qfloat16::operator float() const Q_DECL_NOTHROW
 {