MIPS: Unconditionally specify '-EB' or '-EL'

MIPS: Unconditionally specify '-EB' or '-EL'

This was all done to work around a GCC bug that has been fixed after
4.2. The kernel requires GCC 4.6 or newer so remove all of these hacks
and just use the traditional flags.

 $ mips64-linux-gcc --version | head -n1
 mips64-linux-gcc (GCC) 4.6.3

 $ mips64-linux-gcc -EB -dM -E -C -x c /dev/null | grep MIPSE
 #define MIPSEB 1
 #define __MIPSEB__ 1
 #define _MIPSEB 1
 #define __MIPSEB 1

 $ mips64-linux-gcc -EL -dM -E -C -x c /dev/null | grep MIPSE
 #define __MIPSEL__ 1
 #define MIPSEL 1
 #define _MIPSEL 1
 #define __MIPSEL 1

This is necessary when converting the MIPS VDSO to use $(LD) instead of
$(CC) to link because the OUTPUT_FORMAT is defaulted to little endian
and only flips to big endian when '-EB' is set on the command line.
There is no issue currently because the compiler explicitly passes
'-EB' or '-EL' to the linker regardless of whether or not it was
provided by the user. Passing '-v' to VDSO_LDFLAGS shows:

<gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/collect2 ... -EB ...

even though '-EB' is nowhere to be found in KBUILD_CFLAGS. The VDSO
Makefile already supports getting '-EB' or '-EL' from KBUILD_CFLAGS
through a filter directive but '-EB' or '-EL' is not always present.

If we do not do this, we will see the following error when compiling
for big endian:

$ make -j$(nproc) ARCH=mips CROSS_COMPILE=mips64-linux- \
  64r2el_defconfig arch/mips/vdso/
...
mips64-linux-ld: arch/mips/vdso/elf.o: compiled for a big endian system
and target is little endian
mips64-linux-ld: arch/mips/vdso/elf.o: endianness incompatible with that
of the selected emulation
mips64-linux-ld: failed to merge target specific data of file
arch/mips/vdso/elf.o
...

Remove this legacy hack and just use '-EB' and '-EL' unconditionally.

Reported-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>