Use a map to cache the ModuleType information, so we can do logarithmic

Use a map to cache the ModuleType information, so we can do logarithmic
lookups instead of linear time lookups.  This speeds up bc parsing of a
large file from

137.834u 118.256s 4:27.96
to
132.611u 114.436s 4:08.53

with a release build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23611 91177308-0d34-0410-b5e6-96231b3b80d8