Use the Itanium ABI for thread_local on Darwin.

After some discussion, it was decided to use the Itanium ABI for thread_local on
Darwin OS X platforms. This involved a couple of changes. First, we use
"_tlv_atexit" instead of "__cxa_thread_atexit". Secondly, the global variables
are marked with 'internal' linkage, because we want all access to be calls to
the Itanium-specific entry point, which has normal linkage.
<rdar://problem/13733006>


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@180941 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Don't try to evaluate MaterializeTemporaryExpr as a constant.

...and don't consider '0' to be a null pointer constant if it's the
initializer for a float!

Apparently null pointer constant evaluation looks through both
MaterializeTemporaryExpr and ImplicitCastExpr, so we have to be more
careful about types in the callers. For RegionStore this just means giving
up a little more; for ExprEngine this means handling the
MaterializeTemporaryExpr case explicitly.

Follow-up to r180894.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@180944 91177308-0d34-0410-b5e6-96231b3b80d8