compiler: Recognize libgcc_s regardless of target ABI.

The real libgcc_s is a compiler-provided library; it works just fine with both
glibc and musl. There's no reason that I can see for this check to be limited to
glibc-based targets.

src/target.zig

@@ -261,7 +261,7 @@ pub fn supportsReturnAddress(target: std.Target) bool {
 pub const CompilerRtClassification = enum { none, only_compiler_rt, only_libunwind, both };
 
 pub fn classifyCompilerRtLibName(target: std.Target, name: []const u8) CompilerRtClassification {
-    if (target.abi.isGnu() and std.mem.eql(u8, name, "gcc_s")) {
+    if (std.mem.eql(u8, name, "gcc_s")) {
         // libgcc_s includes exception handling functions, so if linking this library
         // is requested, zig needs to instead link libunwind. Otherwise we end up with
         // the linker unable to find `_Unwind_RaiseException` and other related symbols.