Rollup merge of #143752 - pmur:murp/no-panic-detect-wasi-cc, r=Kobzol

Don't panic if WASI_SDK_PATH not set when detecting compiler

The fedora packaging builds the wasm sysroot outside of the rust build system. Fedora applies a couple of patches related to wasm which I think make this possible. Not panicking seems consistent with the detection logic of other targets when they cannot find cc.

Author: samueltardieu