[Driver] Allow enum SanitizerOrdinal to represent more than 64 different sanitizer checks, NFC.

enum SanitizerOrdinal has reached maximum capacity, this change extends the capacity to 128 sanitizer checks.
This can eventually allow us to add gcc 8's options "-fsanitize=pointer-substract" and "-fsanitize=pointer-compare".

Fixes: https://llvm.org/PR39425

Differential Revision: https://reviews.llvm.org/D57914

llvm-svn: 354873