[analyzer] Don't crash even when the system functions are redefined.
(Applied changes to CStringAPI, Malloc, and Taint.)

This might almost never happen, but we should not crash even if it does.
This fixes a crash on the internal analyzer buildbot, where postgresql's
configure was redefining memmove (radar://11219852).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154451 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed