Move EmitBranchOnBoolExpr and ConstantFoldsToSimpleInteger to

CodeGenFunction.cpp.  Change VisitConditionalOperator to use
constant fold instead of codegen'ing a constant conditional.

Change ForStmt to use EmitBranchOnBoolExpr, this shrinks
expr.c very slightly to 40239 lines.

llvm-svn: 59113