Build-script command statuses are not checked

[smoelius]

The build scripts use Command::output to run make and llvm-config:

solang/build.rs

Lines 8 to 17 in 32a45ea

	Command::new("make")
	.args(["-C", "stdlib"])
	.output()
	.expect("Could not build stdlib");
	// compile our linker
	let cxxflags = Command::new("llvm-config")
	.args(["--cxxflags"])
	.output()
	.expect("could not execute llvm-config");

However, the status fields of the returned Output structs are not checked. So if either command completes with a non-zero exit code, it will go unnoticed.

Moreover, Command::output has the unfortunate side effect of capturing the output, i.e., stdout and stderr are not forwarded to the terminal. So if an error occurs, it could be hidden.

Would you consider a PR to check the commands' statuses?