Give an error if any of the wrappers can't find cargo, rustc or rustdoc

Fixes #1364

Author: bjorn3

scripts/cargo-clif.rs

@@ -64,7 +64,7 @@ fn main() {
     };
 
     #[cfg(unix)]
-    Command::new("cargo").args(args).exec();
+    panic!("Failed to spawn cargo: {}", Command::new("cargo").args(args).exec());
 
     #[cfg(not(unix))]
     std::process::exit(

scripts/rustc-clif.rs

@@ -30,7 +30,7 @@ fn main() {
     env::set_var("RUSTUP_TOOLCHAIN", env!("TOOLCHAIN_NAME"));
 
     #[cfg(unix)]
-    Command::new("rustc").args(args).exec();
+    panic!("Failed to spawn rustc: {}", Command::new("rustc").args(args).exec());
 
     #[cfg(not(unix))]
     std::process::exit(

scripts/rustdoc-clif.rs

@@ -30,7 +30,7 @@ fn main() {
     env::set_var("RUSTUP_TOOLCHAIN", env!("TOOLCHAIN_NAME"));
 
     #[cfg(unix)]
-    Command::new("rustdoc").args(args).exec();
+    panic!("Failed to spawn rustdoc: {}", Command::new("rustdoc").args(args).exec());
 
     #[cfg(not(unix))]
     std::process::exit(