Auto merge of #125411 - onur-ozkan:sanity-check-libstdc++, r=Mark-Simulacrum

check host's libstdc++ version when using ci llvm

If the host's libstdc++ version is too old using ci-llvm may result in an ABI mismatch between the local libstdc++ and libLLVM.so. This PR adds a sanity check to immediately fail at the beginning of the bootstrap before starting the actual build. I am not sure if '8' is the best threshold, but it should be a good start and we can increase it anytime if needed.

Fixes #123037

src/tools/libcxx-version/main.cpp

@@ -0,0 +1,26 @@
+// Detecting the standard library version manually using a bunch of shell commands is very
+// complicated and fragile across different platforms. This program provides the major version
+// of the standard library on any target platform without requiring any messy work.
+//
+// It's nothing more than specifying the name of the standard library implementation (either libstdc++ or libc++)
+// and its major version.
+
+#include <iostream>
+
+int main() {
+    #ifdef _GLIBCXX_RELEASE
+        std::cout << "libstdc++ version: " << _GLIBCXX_RELEASE << std::endl;
+    #elif defined(_LIBCPP_VERSION)
+        // _LIBCPP_VERSION follows "XXYYZZ" format (e.g., 170001 for 17.0.1).
+        // ref: https://github.com/llvm/llvm-project/blob/f64732195c1030ee2627ff4e4142038e01df1d26/libcxx/include/__config#L51-L54
+        //
+        // Since we use the major version from _GLIBCXX_RELEASE, we need to extract only the first 2 characters of _LIBCPP_VERSION
+        // to provide the major version for consistency.
+        std::cout << "libc++ version: " << std::to_string(_LIBCPP_VERSION).substr(0, 2) << std::endl;
+    #else
+        std::cerr << "Coudln't recognize the standard library version." << std::endl;
+        return 1;
+    #endif
+
+    return 0;
+}

src/tools/tidy/src/walk.rs

@@ -16,6 +16,7 @@ pub fn filter_dirs(path: &Path) -> bool {
         "library/stdarch",
         "src/tools/cargo",
         "src/tools/clippy",
+        "src/tools/libcxx-version",
         "src/tools/miri",
         "src/tools/rust-analyzer",
         "src/tools/rustc-perf",