Bug 1025100: Factor out redundant LExtractElement classes; r=sunfish
Bug 1025100: Implement MSimdInsertElement; r=sunfish
Bug 1025100: Use INSERTPS for inserting float elements when SSE4.1 is available; r=sunfish
Bug 1025100: SIMD: add support for with{X,Y,Z,W} in Odin; r=luke