X86: implement functions to analyze & synthesize CMOV|SET|Jcc

getCondFromSETOpc, getCondFromCMovOpc, getSETFromCond, getCMovFromCond

No functional change intended.
If we want to update the condition code of CMOV|SET|Jcc, we first analyze the
opcode to get the condition code, then update the condition code, finally
synthesize the new opcode form the new condition code.

llvm-svn: 159955