Misc compiler-rt fixes. Clarify neg implementations to show what is

actually happening.  Fix mod implementation so it doesn't get 
optimized to a recursive call.  Make x86-32 non-SSE2 shift 
implementation use shld/shrd instead of emulating it (the only x86 processor
where the emulation might be remotely close to justifiable is the Pentium 4).

llvm-svn: 74756