Remove builtin attribute from calls whose targets we replace

If we are replacing a function with the nobuiltin attribute, it may be called
with the builtin attribute on call sites. Remove any such attributes since it's
illegal to have a builtin call to something other than a nobuiltin function.

This fixes the current buildbot breakage (where LLDB crashes on
"expression new foo(42)").



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@186990 91177308-0d34-0410-b5e6-96231b3b80d8