diff --git a/library/std/build.rs b/library/std/build.rs
index 359ae4f20eea8..a8009f28e3a9b 100644
--- a/library/std/build.rs
+++ b/library/std/build.rs
@@ -104,7 +104,7 @@ fn main() {
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
-        ("x86_64", "windows") => false,
+        ("x86_64", "windows") if target_env == "gnu" => false,
         // Apple has a special ABI for `f16` that we do not yet support
         // FIXME(builtins): fixed by <https://github.com/rust-lang/compiler-builtins/pull/675>
         ("x86" | "x86_64", _) if target_vendor == "apple" => false,
@@ -116,10 +116,9 @@ fn main() {
         ("riscv32" | "riscv64", _) => false,
         // Most OSs are missing `__extendhfsf` and `__truncsfhf`
         (_, "linux" | "macos") => true,
-        // Almost all OSs besides Linux and MacOS are missing symbols until compiler-builtins can
-        // be updated. <https://github.com/rust-lang/rust/pull/125016> will get some of these, the
-        // next CB update should get the rest.
-        _ => false,
+        // todo: only for testing, this line will wind up changed as part of
+        // <https://github.com/rust-lang/rust/pull/129385>.
+        _ => true,
     };
 
     let has_reliable_f128 = match (target_arch.as_str(), target_os.as_str()) {
@@ -135,10 +134,10 @@ fn main() {
         // ABI unsupported  <https://github.com/llvm/llvm-project/issues/41838>
         ("sparc", _) => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
-        ("x86_64", "windows") => false,
+        ("x86_64", "windows") if target_env == "gnu" => false,
         // 64-bit Linux is about the only platform to have f128 symbols by default
         (_, "linux") if target_pointer_width == 64 => true,
-        // Same as for f16, except MacOS is also missing f128 symbols.
+        // Almost all OSs are missing symbol. compiler-builtins will have to add them.
         _ => false,
     };