Fix a minor bug in lexing pp-numbers with digit separators: if a pp-number contains "'e+", the pp-number ends between the 'e' and the '+'.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202533 91177308-0d34-0410-b5e6-96231b3b80d8
Tests for lexing of digit separators versus UCNs.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202534 91177308-0d34-0410-b5e6-96231b3b80d8