[x86] fix mappings of cvttp2si/cvttp2ui x86 intrinsics to x86-specific nodes...

[x86] fix mappings of cvttp2si/cvttp2ui x86 intrinsics to x86-specific nodes and isel patterns (PR37551)

Summary:
The tests in:
https://bugs.llvm.org/show_bug.cgi?id=37751
...show miscompiles because we wrongly mapped and folded x86-specific intrinsics into generic DAG nodes.

This patch corrects the mappings in X86IntrinsicsInfo.h and adds isel matching corresponding to the new patterns. The complete tests for the failure cases should be in avx-cvttp2si.ll and sse-cvttp2si.ll and avx512-cvttp2i.ll

Reviewers: RKSimon, gbedwell, spatel

Reviewed By: spatel

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D47993

llvm-svn: 334685