[analyzer] Functions marked __attribute__((const)) don't modify any memory.

This applies to __attribute__((pure)) as well, but 'const' is more interesting
because many of our builtins are marked 'const'.

PR19661

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208154 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Use a lazily-initialized BugType in ObjCSelfInitChecker.

Follow-up to Nico's leak-stopping patch in r208110.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208155 91177308-0d34-0410-b5e6-96231b3b80d8