Fix wchar.cpp MIPS narrowing conversion build failure.

Change-Id: Id9103c78958d60337dbdb807b11256c1b31c632a
Merge "Fix wchar.cpp MIPS narrowing conversion build failure."
Fix wchar_t signedness problems found on x86-64.

The existing tests caught this.

Change-Id: I6269844ae4301fd2c596241a59e97eb67ef166fa
Merge "Fix wchar_t signedness problems found on x86-64."
Merge remote-tracking branch 'aosp/master' into fml-master