[clang-scan-deps] Dependency directives source minimizer:

single quotes are not digit separators after a valid character literal prefix

The single quote character can act as a c++ digit separator.
However, the minimizer shouldn't treat it as such when it's actually following
a valid character literal prefix, like L, U, u, or u8.

Differential Revision: https://reviews.llvm.org/D64525

llvm-svn: 365700