fix(build): drop explicit -lc++abi from the test stdlib link

libc++.1.dylib reexports its abi; linking libc++abi.dylib explicitly
alongside the system abi (loaded transitively via macOS frameworks)
doubled the __cxa_* runtime state — every test binary aborted before
main (exit 6) on the first macOS CI round.

Author: Sunrisepeak

src/build/flags.cppm

@@ -402,8 +402,13 @@ CompileFlags compute_flags(const BuildPlan& plan) {
             auto libDir = llvmRootForStdlib / "lib";
             if (std::filesystem::exists(libDir / "libc++.dylib")
                 || std::filesystem::exists(libDir / "libc++.1.dylib")) {
+                // No explicit -lc++abi: libc++.1.dylib reexports its abi,
+                // and adding the abi dylib EXPLICITLY next to the system one
+                // (pulled in transitively by macOS frameworks) doubles the
+                // __cxa_* runtime state — every binary aborted at load
+                // (SIGABRT before main) on the first CI round of this fix.
                 f.ldStdlibTest = " -nostdlib++ -L" + escape_path(libDir)
-                               + " -lc++ -lc++abi"
+                               + " -lc++"
                                + " -Wl,-rpath," + escape_path(libDir);
             }
         }