[X86][SSE] Replace 128-bit SSE41 PMOVSX intrinsics with native IR

128-bit vector integer sign extensions correctly lower to the pmovsx instructions even for debug builds.

This patch removes the builtins and reimplements the _mm_cvtepi*_epi* intrinsics __using builtin_shufflevector (to extract the bottom most subvector) and __builtin_convertvector (to actually perform the sign extension).

Differential Revision: http://reviews.llvm.org/D12835

llvm-svn: 248092