Subzero: don't assert about lack of atomic load/store on x86
Subzero: don't assert about lack of atomic load/store on x86

On x86-32/64, assume that loads and stores are atomic, and that
strictest memory order is supported.

Bug: b/150475088
Change-Id: I5f99a0309eca668d0c1197387bcf687b32381179
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/41790
Tested-by: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader