TypePrinter print __restrict if not in C99 mode

restrict is a keyword in C99 but not in C++ while clang accepts __restrict for C++ code. Modify the TypePrinter to print __restrict when not processing C99 code.

Printing restrict in C++ was problematic as printing the argument of
  int f(int * __restrict a) { ... }
resulted in
  int *restrict a
which is incorrect.

http://reviews.llvm.org/D8048

llvm-svn: 231179