Treat LLVM libc's dynamic loader as the GNU ABI, which LLVM libc keeps, rather
than falling back to musl.

--- a/lib/std/zig/system.zig
+++ b/lib/std/zig/system.zig
@@ -634,6 +634,9 @@
                             result.abi = ld_info.abi;
                             break;
                         }
+                    } else if (std.mem.startsWith(u8, fs.path.basename(full_ld_path), "ld-llvm-libc")) {
+                        // LLVM libc keeps the glibc ABI
+                        result.abi = .gnu;
                     }
                 }
             },