Re-code the saving of the gp register for MIPS64 so it compiles under
recent versions of gcc.
Use assembler directives to perform the gp register save/restore.
Simply remove the additional GP register saves for MIPS64, as
they appear to be unnecessary.
Clean up stray extra include from prior versions.
Add back in the explicit save/restore, in case there is a
situation where the compiler does not automatically save it
for us.  Eliminate the special handling for N32 ABI, as registers
are still 64 bits in that case.
Merge pull request #58 from madisongh/master

Re-code the saving of the gp register for MIPS64 so it compiles