QNX: Fix -developer-build

-developer-build enables -Werror=undef, which uncovered a bug inside
qcompilerdetection.h.

According to the Dinkum headers, it is necessary to account for three different states
concerning the values of the _HAS_* macros:

    1. undefined
    2. 0
    3. 1

Therefore, it is necessary to check both whether it is defined and if it is
not 0. Only checking whether a given macro is 0 will generate a trap by
-Werror=undef.

(__GLIBCXX__ is the sole exception).

Change-Id: Ib95e485698ee38858a1671d930d7e960b75bb041
Reviewed-by: James McDonnell <jmcdonnell@qnx.com>
Reviewed-by: Dan Cape <dcape@qnx.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qcompilerdetection.h

@@ -931,8 +931,8 @@
 // Older versions (QNX 650) do not support C++11 features
 // _HAS_* macros are set to 1 by toolchains that actually include
 // Dinkum C++11 libcpp.
-#  if !__GLIBCXX__
-#   if !_HAS_CPP0X
+#  if !defined(__GLIBCXX__)
+#   if !defined(_HAS_CPP0X) || !_HAS_CPP0X
 // Disable C++11 features that depend on library support
 #    undef Q_COMPILER_INITIALIZER_LISTS
 #    undef Q_COMPILER_RVALUE_REFS
@@ -940,10 +940,10 @@
 #    undef Q_COMPILER_UNICODE_STRINGS
 #    undef Q_COMPILER_NOEXCEPT
 #   endif // !_HAS_CPP0X
-#   if !_HAS_NULLPTR_T
+#   if !defined(_HAS_NULLPTR_T) || !_HAS_NULLPTR_T
 #    undef Q_COMPILER_NULLPTR
 #   endif //!_HAS_NULLPTR_T
-#   if !_HAS_CONSTEXPR
+#   if !defined(_HAS_CONSTEXPR) || !_HAS_CONSTEXPR
 // The libcpp is missing constexpr keywords on important functions like std::numeric_limits<>::min()
 // Disable constexpr support on QNX even if the compiler supports it
 #    undef Q_COMPILER_CONSTEXPR