feat(native-engine) Panic if gcc/clang-10 is missing

[Hywan]

When gcc or clang-10 is absent, we get a non-obvious error:

Compilation error: No such file or directory (os error 2)

It comes from

wasmer/lib/engine-native/src/artifact.rs

Lines 288 to 298 in 2cd1221

	let output = Command::new(linker)
	.arg(&filepath)
	.arg("-o")
	.arg(&shared_filepath)
	.args(&target_args)
	// .args(&wasmer_symbols)
	.arg("-shared")
	.args(&cross_compiling_args)
	.arg("-v")
	.output()
	.map_err(to_compile_error)?;

.

This PR improves that by panicking when gcc or clang isn't present.

[syrusakbary]

bors r+

[bors]

Build succeeded:

• Audit
• Code lint
• Test on linux
• Test on macos
• Test on windows