MIPS: fix symbol naming for `mips_lock', `mips_local_resume', and `mips_local_addr_space_init'

Properly export the symbol names also on MIPS. `make check' was
complaining:

src/.libs/libunwind.a(Linit.o): In function `mips_local_addr_space_init':
src/mips/Ginit.c:183: multiple definition of `mips_local_addr_space_init'
../src/.libs/libunwind-mips.a(Ginit.o):src/mips/Ginit.c:183: first defined here

src/.libs/libunwind.a(Lglobal.o): In function `_ULmips_init':
src/mips/Gglobal.c:42: multiple definition of `mips_lock'
../src/.libs/libunwind-mips.a(Gglobal.o):src/mips/Gglobal.c:42: first defined here

collect2: ld returned 1 exit status
1 file changed