[Sema] Change addr space diagnostics in casts to follow C++ style.

[Sema] Change addr space diagnostics in casts to follow C++ style.

This change adds a new diagnostic for mismatching address spaces
to be used for C++ casts (only enabled in C style cast for now,
the rest will follow!).

The change extends C-style cast rules to account for address spaces.
It also adds a separate function for address space cast checking that
can be used to map from a separate address space cast operator
addrspace_cast (to be added as a follow up patch).

Note, that after this change clang will no longer allows arbitrary
address space conversions in reinterpret_casts because they can lead
to accidental errors. The implicit safe conversions would still be
allowed.

Differential Revision: https://reviews.llvm.org/D58346

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@355609 91177308-0d34-0410-b5e6-96231b3b80d8