Update libm-test/build.rs to skip directories

Don't try to generate tests for directories, or for files that contain
`f16` or `f128` (as these types are not provided by musl's math
implementations).

(cherry picked from commit 76f84e6)

Author: tgross35

crates/libm-test/build.rs

@@ -63,6 +63,7 @@ mod musl_reference_tests {
         let files = fs::read_dir(math_src)
             .unwrap()
             .map(|f| f.unwrap().path())
+            .filter(file_needs_test)
             .collect::<Vec<_>>();
 
         let mut math = Vec::new();
@@ -94,6 +95,19 @@ mod musl_reference_tests {
         generate_unit_tests(&math);
     }
 
+    /// Check whether a path within `src/math` should get tests generated.
+    fn file_needs_test(path: &PathBuf) -> bool {
+        // Skip directories
+        if path.is_dir() {
+            return false;
+        }
+
+        let fname = path.file_name().unwrap().to_str().unwrap();
+
+        // Musl doesn't support `f16` or `f128`
+        !(fname.contains("f16") || fname.contains("f128"))
+    }
+
     /// A "poor man's" parser for the signature of a function
     fn parse(s: &str) -> Function {
         let s = eat(s, "pub fn ");