Define Q_CC_CLANG to be the version of upstream Clang that's in use

We map the Apple Clang versions to upstream, so that we have one
define to compare against.

Fixes build break on iOS due to qbasicatomic.h not defining
QT_BASIC_ATOMIC_HAS_CONSTRUCTORS on Apple Clang versions, which
is needed after 1e9db9f5e18123f2e686c10b

Change-Id: I17493c0187c20abc5d22e71944d62bfd16afbad2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Store the GCC version number in Q_CC_GNU

The sequence of (__GNUC__ * 100 + __GNUC_MINOR__) was used in quite a
few places. Simplify it to make the code more readable.

This follows the change done for Clang, which was quite necessary since
Apple's version of Clang has different build numbers.

Change-Id: I886271a5a5f21ae59485ecf8d140527723345a46
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Define the Intel compiler and Microsoft C++ versions in the Q_CC_ macros

This is for completeness, since we've done the same for Q_CC_GNU and
Q_CC_CLANG. We won't really use the macros like this because both
__INTEL_COMPILER and _MSC_VER are readily usable.

Change-Id: I669c60166fa4839d43f84f339e6896321d62817f
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>