Merge pull request dotnet/coreclr#4795 from sivarv/simdret

[x64 Unix] Avoid SIMD types returned in two return registers from requiring to go through memory.

Commit migrated from https://github.com/dotnet/coreclr/commit/b3be35f379519120acd8427485524e92cf911918

diff --cc src/coreclr/src/jit/codegenxarch.cpp
Simple merge

diff --cc src/coreclr/src/jit/importer.cpp
Simple merge