MIPS64: Fix macro-assembler GC related routines in generated code.

Fixes assertion failures and random crashes after GC cycle.

 Fatal error in ../src/spaces.cc, line 1201
 CHECK((black_size) <= (page->LiveBytes())) failed

TEST=test/mjsunit/debug-setbreakpoint.js
BUG=
MIPS64: Clean lithium codegen.

Remove redundant lithium instruction.
MIPS64: Clean build system related to arch variant flag.

TEST=
BUG=
MIPS64: Remove redundant functions for checking integer range.

TEST=
BUG=
MIPS64: Fix debug build, use is_int16 instead obsolete is_int64_16.
MIPS64: Remove unnecessary sign extension.

Also fix compile warnings on some printouts.

TEST=