Rename variables in SemaExpr.cpp to give a more consistant naming scheme.

ExprResult LHS, RHS,
Expr *LHSExpr, *RHSExpr
QualType LHSType, RHSType

Functions changed:
checkEnumComparison()
diagnoseDistinctPointerComparison()
convertPointersToCompositeType()
diagnoseFunctionPointerToVoidComparison()

llvm-svn: 139184