[NFC] Fix usage of Builder.insert(new Bitcast...)in CodeGenFunction

This is exactly a "CreateBitCast", so refactor this to get rid of a
'new'.

Note that this slightly changes the test, as the Builder is now
seemingly smart enough to fold one of the bitcasts into the annotation
call.

Change-Id: I1733fb1fdf91f5c9d88651067130b9a4e7b5ab67

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@349506 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed