Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1509

WASI is similar to emscripten, providing a syscall layer to WebAssembly focused on server side applications. There are some config knobs that are in place to allow building the repo for emscripten which also need to support wasi (as built with LLVM). Aside from that, there are still some features it supports less than escripten, for example related to signals, causing the build to be even more limited for it.
Merge ec9fa081609687035005dfdafd312754f31c3fbb into 861e53c8

Merging this change closes #1509

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1509 from anuraaga:wasi-sdk-build ec9fa081609687035005dfdafd312754f31c3fbb
PiperOrigin-RevId: 557166498
Change-Id: Ic51149d8b092fd888c9a5c383275257fc8ff4232