Rollup merge of rust-lang#38493 - sanxiyn:filecheck, r=alexcrichton

Find FileCheck using llvm-config

This allows using system LLVM from Debian package to run codegen tests.

Fix rust-lang#36282.

r? @alexcrichton

src/bootstrap/lib.rs

@@ -721,7 +721,8 @@ impl Build {
     fn llvm_filecheck(&self, target: &str) -> PathBuf {
         let target_config = self.config.target_config.get(target);
         if let Some(s) = target_config.and_then(|c| c.llvm_config.as_ref()) {
-            s.parent().unwrap().join(exe("FileCheck", target))
+            let llvm_bindir = output(Command::new(s).arg("--bindir"));
+            Path::new(llvm_bindir.trim()).join(exe("FileCheck", target))
         } else {
             let base = self.llvm_out(&self.config.build).join("build");
             let exe = exe("FileCheck", target);

src/bootstrap/sanity.rs

@@ -143,7 +143,7 @@ pub fn check(build: &mut Build) {
     // Externally configured LLVM requires FileCheck to exist
     let filecheck = build.llvm_filecheck(&build.config.build);
     if !filecheck.starts_with(&build.out) && !filecheck.exists() && build.config.codegen_tests {
-        panic!("filecheck executable {:?} does not exist", filecheck);
+        panic!("FileCheck executable {:?} does not exist", filecheck);
     }
 
     for target in build.config.target.iter() {