ubsan: Only emit constants for filenames and type descriptors once.

Produces neater IR in significantly less time.

(~18% faster -O0 compile time for sqlite3 with -fsanitize=undefined)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194231 91177308-0d34-0410-b5e6-96231b3b80d8