librustc: Fixed issues arising due to PNaCl toolchain changes.
compiletest: Removed pnacl-translate hacks due to 'frem' instructions.
libstd: Redirect calls to _Unwind_Backtrace and _Unwind_GetIP* to
abort. Obviously this breaks things, however they cause unresolved references at
translation time so this is a dirty fix until I have time to (somehow) implement
backtraces without using them.