QtWebEngine incorrect pass cflags when QMAKE_CFLAGS contains MIPS GCC flags (for example: -march=mips32r5 -mtune=p5600)

In the Qt build system there are some issues related to passing CFLAGS to the QtWebEngine build system during the process of building whole Qt (when the parameter -skip qtwebengine is not used). Qt build system reads the contents of QMAKE_CFLAGS and declare ninja variables according to found options. If we consider the qtwebengine/src/core/gyp_run.pro we can find the code for parsing QMAKE_CFLAGS contains. For example, when we deal to MIPS architecture the code of gyp_run.pro trying to find the "mips32r2" substring in the value of QMAKE_CFLAGS variable:

contains(QMAKE_CFLAGS, "mips32r2"): mips_arch_variant=\"r2\"

But in the QMAKE_CFLAGS variable the contains() function cannot find "mips32r2" string because the GCC option can be "-march=mips32r2". Also in the code above we have to add mips_arch_variant variable into GYP_CONFIG. So the correct code should be loke follow:

contains(QMAKE_CFLAGS, "-march=mips32r2"): GYP_CONFIG += mips_arch_variant=\"r2\"

Further created ninja variables are processed in the file qtwebengine/src/3rdparty/chromium/build/common.gypi where we also can see incorrect or not fulfill behaviour.

Also the files qtwebengine/src/core/gyp_run.pro and qtwebengine/src/3rdparty/chromium/build/common.gypi do not contains any handlers for mips32r5 architecture. For example to tune compilation for the P5600 architecture we have to pass the following options to GCC-5.3.0

$ ${CROSS_COMPILE}gcc -march=mips32r5 -mtune=p5600

For GCC-5.4.0 we can simplify our controls to the only one option: -march=p5600.

Please considere the attached patch and make decision about improvement the WebEngine build system.