third_party/marl: Implement page-based functions for Fuchsia
third_party/marl: Implement page-based functions for Fuchsia

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/+/37131
Reviewed-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>
Tested-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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