Added sanity check to bootstrap to hard error on wasm builds without
clang, and changed distribution image `dist-various-2` to use clang to
build for official targets.

Also fixed a typo in the sanity check for bootstrap, as we are checking for clang-likeness in every wasm target.

Fix host code appearing in Wasm binaries

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This is a direct fix for issue [132802](#132802).
Followed the outline as follows:
> * give a hard error in bootstrap when using gcc to compile for wasm
> * change our CI to use clang instead of gcc
> * add a test that compiling a sample program for wasm32-unknown doesn't give any linker warnings

The `test-various` ci job was also changed.

try-job: test-various
try-job: dist-various-1
try-job: dist-various-2
try-job: x86_64-msvc-1