Fix host ABI detection with MinGW 4.6.

Fix warning: "Unable to completely determine the host ABI
(x86-windows-unknown-pe-32bit).". It seems mingw32 is no longer
defined in MinGW 4.6; use the more reliable Q_CC_MINGW.

Change-Id: I2d4f84a62b2fe829b3a8d755a76429b94c0109f5
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>

src/plugins/projectexplorer/abi.cpp

@@ -643,7 +643,7 @@ Abi Abi::hostAbi()
     subos = WindowsMsvc2008Flavor;
 #elif _MSC_VER == 1400
     subos = WindowsMsvc2005Flavor;
-#elif defined (mingw32)
+#elif defined (Q_CC_MINGW)
     subos = WindowsMSysFlavor;
 #endif
     format = PEFormat;