Fix syntax error

Author: tgross35

library/std/build.rs

@@ -150,8 +150,12 @@ fn main() {
             // LLVM lowers `fp128` math to `long double` symbols even on platforms where
             // `long double` is not IEEE binary128. See
             // <https://github.com/llvm/llvm-project/issues/44744>.
+            // This rules out any <= 32-bit plaftofms because their `long double` is `f64`, as well
+            // as anything other than Linux for the same reason. `x86` has 80-bit `long double` so
+            // also suffers from the problem.
             ("x86_64", _) => false,
-            _ => true,
+            (_, "linux") if target_pointer_width == 64 => true,
+            _ => false,
         };
 
     if has_reliable_f16 {

library/std/src/f128/tests.rs

@@ -447,7 +447,7 @@ fn test_powf() {
     assert_eq!(1.0f128.powf(1.0), 1.0);
     assert_approx_eq!(3.4f128.powf(4.5), 246.40818323761892815995637964326426756, TOL_P2);
     assert_approx_eq!(2.7f128.powf(-3.2), 0.041652009108526178281070304373500889273, TOL_N2);
-    assert_approx_eq!((-3.1f128).powf(2.0), 9.61000000000000055067062021407765193876 TOL_P2);
+    assert_approx_eq!((-3.1f128).powf(2.0), 9.6100000000000005506706202140776519387, TOL_P2);
     assert_approx_eq!(5.9f128.powf(-2.0), 0.028727377190462507313100483690639638451, TOL_N2);
     assert_eq!(8.3f128.powf(0.0), 1.0);
     assert!(nan.powf(2.0).is_nan());