fix(elb): use clang-only -fbracket-depth flag conditionally

gcc rejects -fbracket-depth=1024 with 'unrecognized command-line option'.
Use shell subshell to probe cc --version and only pass the flag when
the compiler is clang.

lang/elb.el

@@ -271,7 +271,10 @@ fn link_binary(c_files: [String], out_bin: String, runtime_path: String, out_dir
     let parts: [String] = native_list_empty()
     // Include both the runtime dir (for el_runtime.h) and the output dir
     // (for module.elh cross-module forward declarations).
-    let parts = native_list_append(parts, "cc -O2 -fbracket-depth=1024 -I " + dirname_of(runtime_path) + " -I " + out_dir)
+    // Detect clang vs gcc: -fbracket-depth is clang-only; silently ignored
+    // if unsupported but gcc rejects it with an error.
+    let bracket_flag: String = "$(cc --version 2>&1 | grep -q clang && printf -- '-fbracket-depth=1024' || true)"
+    let parts = native_list_append(parts, "cc -O2 " + bracket_flag + " -I " + dirname_of(runtime_path) + " -I " + out_dir)
     let i = 0
     while i < n {
         let f: String = native_list_get(c_files, i)