MIPS64: Fix bugs in safepoints and DoDeferredNumberTagIU.

TEST=mjsunit/compiler/uint32.js,  mjsunit/regress/regress-82769,
mjsunit/eval-stack-trace, mjsunit/function-names
MIPS64: Fix compiler warning for gxx version 4.6.4.

TEST=
MIPS64: Removed excess function for sign-extension.

TEST=
MIPS64: Clean constants-mips64, deoptimizer-mips64