Disable f16 on platforms that have recursion problems

CI in [1] seems to indicate that there are cases where the `f16`
infinite recursion bug ([2], [3]) can make its way into what gets called
during tests, even though this doesn't seem to be the usual case. In
order to make sure that we avoid these completely, just unset
`f16_enabled` on any platforms that have the recursion problem.

This also refactors the `match` statement to be more in line with
`library/std/build.rs`.

[1]: rust-lang#729
[2]: llvm/llvm-project#97981
[3]: rust-lang#651

configure.rs

@@ -51,31 +51,46 @@ impl Target {
 /// Configure whether or not `f16` and `f128` support should be enabled.
 pub fn configure_f16_f128(target: &Target) {
     // Set whether or not `f16` and `f128` are supported at a basic level by LLVM. This only means
-    // that the backend will not crash when using these types. This does not mean that the
-    // backend does the right thing, or that the platform doesn't have ABI bugs.
+    // that the backend will not crash when using these types and generates code that can be called
+    // without crashing (no infinite recursion). This does not mean that the platform doesn't have
+    // ABI or other bugs.
     //
     // We do this here rather than in `rust-lang/rust` because configuring via cargo features is
     // not straightforward.
     //
     // Original source of this list:
     // <https://github.com/rust-lang/compiler-builtins/pull/652#issuecomment-2266151350>
-    let (f16_ok, f128_ok) = match target.arch.as_str() {
-        // `f16` and `f128` both crash <https://github.com/llvm/llvm-project/issues/94434>
-        "arm64ec" => (false, false),
-        // `f16` crashes <https://github.com/llvm/llvm-project/issues/50374>
-        "s390x" => (false, true),
-        // FIXME(llvm): `f16` test failures fixed by <https://github.com/llvm/llvm-project/pull/107791>
-        "loongarch64" => (false, true),
-        // `f128` crashes <https://github.com/llvm/llvm-project/issues/96432>
-        "mips64" | "mips64r6" => (true, false),
-        // `f128` crashes <https://github.com/llvm/llvm-project/issues/101545>
-        "powerpc64" if &target.os == "aix" => (true, false),
-        // `f128` crashes <https://github.com/llvm/llvm-project/issues/41838>
-        "sparc" => (true, false),
-        // `f16` miscompiles <https://github.com/llvm/llvm-project/issues/96438>
-        "wasm32" | "wasm64" => (false, true),
+    let f16_enabled = match target.arch.as_str() {
+        // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
+        "arm64ec" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/50374>
+        "s390x" => false,
+        // Infinite recursion <https://github.com/llvm/llvm-project/issues/97981>
+        // FIXME(llvm): loongarch fixed by <https://github.com/llvm/llvm-project/pull/107791>
+        "csky" => false,
+        "hexagon" => false,
+        "loongarch64" => false,
+        "mips" | "mips64" | "mips32r6" | "mips64r6" => false,
+        "powerpc" | "powerpc64" => false,
+        "sparc" | "sparc64" => false,
+        "wasm32" | "wasm64" => false,
         // Most everything else works as of LLVM 19
-        _ => (true, true),
+        _ => true,
+    };
+
+    let f128_enabled = match target.arch.as_str() {
+        // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
+        "arm64ec" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/96432>
+        "mips64" | "mips64r6" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/95471>
+        "nvptx64" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/101545>
+        "powerpc64" if &target.os == "aix" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/41838>
+        "sparc" => false,
+        // Most everything else works as of LLVM 19
+        _ => true,
     };
 
     // If the feature is set, disable these types.
@@ -84,11 +99,11 @@ pub fn configure_f16_f128(target: &Target) {
     println!("cargo::rustc-check-cfg=cfg(f16_enabled)");
     println!("cargo::rustc-check-cfg=cfg(f128_enabled)");
 
-    if f16_ok && !disable_both {
+    if f16_enabled && !disable_both {
         println!("cargo::rustc-cfg=f16_enabled");
     }
 
-    if f128_ok && !disable_both {
+    if f128_enabled && !disable_both {
         println!("cargo::rustc-cfg=f128_enabled");
     }
 }