Make cpp assembly file extensions case sensitive again

This fixes an issue introduced by PR bazelbuild#14005 where .s and .S
extensions were handled case-insensitive on Windows so the action
assemble was triggered instead of preprocess_assemble.

src/main/java/com/google/devtools/build/lib/rules/cpp/CppFileTypes.java

@@ -99,8 +99,8 @@ public ImmutableList<String> getExtensions() {
 
         @Override
         public boolean apply(String path) {
-          return (OS.endsWith(path, ext) && !PIC_ASSEMBLER.matches(path))
-              || OS.endsWith(path, ".asm");
+          return (path.endsWith(ext) && !PIC_ASSEMBLER.matches(path))
+              || path.endsWith(".asm");
         }
 
         @Override