mips32/64: Remove default flags -mips32 and -mips64 from the Makefile.all.am.

During configuration of Valgrind we check does the compiler support -march=mips32 and
-march=mips64. If compiler supports these flags we are using them as default flags for
mips32 and mips64.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13815 a5019735-40e9-0310-863c-91ae7b9d1cf9