[FastISel][X86] Implement the FastLowerCall hook.
[FastISel][X86] Implement the FastLowerCall hook.

This implements the FastLowerCall hook, which is based on the DoSelectCall
function. The implementation is very similar, but the target-independent call
lowering part has been factored out.

This should also enable patchpoint intrinsic lowering for FastISel on X86.

Related to <rdar://problem/17427052>.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@213049 91177308-0d34-0410-b5e6-96231b3b80d8

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