Compile on 10.7: Disable constexpr support

Apple Clang 3.2 is known bad with broken or partial
support. Which version is the first good version is
unknown.

Change-Id: I1b938281680dde5acbe0e08979444b6055a1cc4e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qcompilerdetection.h

@@ -613,7 +613,7 @@
 #    if __has_feature(cxx_strong_enums)
 #      define Q_COMPILER_CLASS_ENUM
 #    endif
-#    if __has_feature(cxx_constexpr)
+#    if __has_feature(cxx_constexpr) && Q_CC_CLANG > 302 /* CLANG 3.2 has bad/partial support */
 #      define Q_COMPILER_CONSTEXPR
 #    endif
 #    if __has_feature(cxx_decltype) /* && __has_feature(cxx_decltype_incomplete_return_types) */