Ask qdoc not to parse Q_DECL_UNUSED

We have it on function declarations and it gets a bit lost...

Change-Id: I19ba2e760f3714c26e78c3d8fd2570af3dcd136e
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
MIPS DSP build system fix and additional optimizations.

Changed MIPS DSP portion of the mkspecs/features/simd.prf file in order
to fix the corrupted build system for MIPS platforms.

List of the additionally optimized functions

from file src/gui/painting/qdrawhelper.cpp:
- qt_blend_rgb16_on_rgb16
- qt_fetchUntransformed_888
- qt_fetchUntransformed_444
- qt_fetchUntransformed_argb8565

from file src/gui/image/qimage.cpp:
- convert_ARGB_to_ARGB_PM_inplace

from file src/corelib/qstring.cpp:
- ucstrncmp
- toLatin1_helper
- fromLatin1_helper

Change-Id: I5c47a69784917eee29a8dbd2718828a390b27c93
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>