-Wc++98-compat warnings for the lexer.

-Wc++98-compat warnings for the lexer.

This also adds a -Wc++98-compat-pedantic for warning on constructs which would
be diagnosed by -std=c++98 -pedantic (that is, it warns even on C++11 features
which we enable by default, with no warning, in C++98 mode).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142034 91177308-0d34-0410-b5e6-96231b3b80d8