qt5webkit: fix build issue with 32-bits armv8-a

Adds WTF platform support for the 32-bits armv8-a architectures.

Fixes:

	In file included from ./config.h:30:0,
	                 from ...
	./wtf/Platform.h:323:6: error: #error "Not supported ARM architecture"
	 #    error "Not supported ARM architecture"
	      ^~~~~
from this defconfig:

BR2_arm=y
BR2_cortex_a72=y
BR2_ARM_FPU_VFPV3D16=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_INIT_NONE=y
BR2_PACKAGE_QT5=y
BR2_PACKAGE_QT5WEBKIT=y

The patch is an adaptation of an upstream fix in version 5.212 of
qtwebkit[1].

Unfortunately, the commit cannot be backported and has to be fixed since
the toolchain does not define __ARM_ARCH_8__ but __ARM_ARCH_8A__.

	$ host/bin/arm-buildroot-linux-gnueabihf-g++ -dM -E - < /dev/null | grep ARM_ARCH
	#define __ARM_ARCH_ISA_ARM 1
	#define __ARM_ARCH_8A__ 1
	#define __ARM_ARCH_PROFILE 65
	#define __ARM_ARCH_ISA_THUMB 2
	#define __ARM_ARCH 8
	#define __ARM_ARCH_EXT_IDIV__ 1

[1]: https://github.com/qt/qtwebkit/blob/35655d5f4bad248ead1700b59c381cc568b4e98b/Source/WTF/wtf/Platform.h#L241-L242



Cc: Arnout Vandecappelle <arnout@mind.be>
Reported-by: Brock Williams <brock@cottonwoodcomputer.com>
Reviewed-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Gaël PORTAY <gael.portay@savoirfairelinux.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>