[StaticAnalyzer] Add missing include to SMTAPI.h. [NFC]

This include is needed for types within SMTAPI.h. (It's very possible that
compilation would succeed without it, but that's only by chance.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@353599 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed