Integers which are too large should be an error.

Switch some warnings over to errors which should never have been warnings
in the first place.  (Also, a minor fix to the preprocessor rules for
integer literals while I'm here.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186903 91177308-0d34-0410-b5e6-96231b3b80d8