This allows users to query the target triple and target pointer width, which
would make me able to fix https://github.com/servo/rust-bindgen/issues/593 and
other related bugs in an elegant way (without having to manually parse the
target triple in the command line arguments).

Differential Revision: https://reviews.llvm.org/D32389



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@301648 91177308-0d34-0410-b5e6-96231b3b80d8