Revert "Absolutify CXX as well as CC (bazelbuild#969)"

This reverts commit b3e26e0.

Author: Shikhar Bhushan

cargo/cargo_build_script_runner/bin.rs

@@ -88,15 +88,13 @@ fn run_buildrs() -> Result<(), String> {
         }
     }
 
-    for compiler_env_var in &["CC", "CXX"] {
-        if let Some(compiler_path) = env::var_os(compiler_env_var) {
-            let mut compiler_path = exec_root.join(compiler_path).into_os_string();
-            if let Some(sysroot_path) = env::var_os("SYSROOT") {
-                compiler_path.push(" --sysroot=");
-                compiler_path.push(&exec_root.join(sysroot_path));
-            }
-            command.env(compiler_env_var, compiler_path);
+    if let Some(cc_path) = env::var_os("CC") {
+        let mut cc_path = exec_root.join(cc_path).into_os_string();
+        if let Some(sysroot_path) = env::var_os("SYSROOT") {
+            cc_path.push(" --sysroot=");
+            cc_path.push(&exec_root.join(sysroot_path));
         }
+        command.env("CC", cc_path);
     }
 
     if let Some(ar_path) = env::var_os("AR") {

test/cargo_build_script/build.rs

@@ -4,24 +4,4 @@ fn main() {
         "cargo:rustc-env=TOOL_PATH={}",
         std::env::var("TOOL").unwrap()
     );
-
-    // Assert that the CC and CXX env vars existed and were executable.
-    // We don't assert what happens when they're executed (in particular, we don't check for a
-    // non-zero exit code), but this asserts that it's an existing file which is executable.
-    //
-    // Unfortunately we need to shlex the path, because we add a `--sysroot=...` arg to the env var.
-    for env_var in &["CC", "CXX"] {
-        let v = std::env::var(env_var)
-            .unwrap_or_else(|err| panic!("Error getting {}: {}", env_var, err));
-        let (path, args) = if let Some(index) = v.find("--sysroot") {
-            let (path, args) = v.split_at(index);
-            (path, Some(args))
-        } else {
-            (v.as_str(), None)
-        };
-        std::process::Command::new(path)
-            .args(args.into_iter())
-            .status()
-            .unwrap();
-    }
 }