Projects using Dawn that are compiled with Emscripten may use some
of our common headers and utilities. ex.) creating a ShaderModule
from SPIR-V. Add handling for __EMSCRIPTEN__ to Platform.h so
compiling to WASM works.
Also, implement GetExecutablePath on Emscripten as unreachable.
This is only ever used to search native paths in the Vulkan backend.
Bug: none
Change-Id: I5d9d6e27e287cb34e7af3214add1c4bc8c6a0f70
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/25064
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>