Mostly copypasta from: src/Reactor/ExecutableMemory.cpp

Will be upstreamed to marl if the autorollers are happy.

Bug: b/140546382
Change-Id: I6cf0dc8638e37f17d097ea645c9a84cef1368a3d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37131Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>