n64/n32 - build support patches

[C. Jayachandran]

I've updated the patches for building n64 and n32 kernel and
userspace,  please review. The patches are:

Tool chain support for n64 and n32::
http://sites.google.com/site/cjayachandran/files/n64-n32-toolchain.patch

This updates the gcc configuration  to provide the default ABI, linker
scripts and endianness flags during n64/n32 and o32 builds. With this
change, we don't need the -Wl, flags for linker emulation, the mabi
flags or the -EB/-EL for compiler.
I had to add a make variable in TARGET_DEFINES in
gnu/usr.bin/cc/Makefile.tgt and use that to pass the defaults while
creating 'tm.h' - this change is not MIPS-specific.

User/kernel build with n64 and n32:
http://sites.google.com/site/cjayachandran/files/n64-n32-build.patch

updated bsd.cpu.mk which does not set LDFLAGS, adds ldscript.mips.n32
and removes unnecessary flags from Makefile.mips.

Thanks,
JC.