cmSystemTools: Fix IsPathToFramework implementation (#15535)

Use more reliable logic to detect if a path ends in ".framework".  The
old logic added by commit v2.4.0~791 (add better support for framework
linking, 2005-12-26) did not account for paths not ending in it at all.
With a 9-character path the logic and "npos == -1" happens to make the
old check pass.

Source/cmSystemTools.cxx

@@ -1486,15 +1486,8 @@ void cmSystemTools::EnableVSConsoleOutput()
 
 bool cmSystemTools::IsPathToFramework(const char* path)
 {
-  if(cmSystemTools::FileIsFullPath(path))
-    {
-    std::string libname = path;
-    if(libname.find(".framework") == libname.size()+1-sizeof(".framework"))
-      {
-      return true;
-      }
-    }
-  return false;
+  return (cmSystemTools::FileIsFullPath(path) &&
+          cmHasLiteralSuffix(path, ".framework"));
 }
 
 bool cmSystemTools::CreateTar(const char* outFileName,