win: Fix the build with verbose options

The 'append' method should be used instead of extend,
since the 'extend' method treats the arguments as an iterable object,
so extends the current list with list of characters.

Author: kaadam

scripts/build_llvm_project.py

@@ -80,7 +80,7 @@ def generate_buildoptions(arguments):
     base_cmake_args.append(f'-DCMAKE_CXX_COMPILER={arguments.cxx}')
 
   if arguments.verbose:
-    base_cmake_args.extend('-DCMAKE_VERBOSE_MAKEFILE=ON')
+    base_cmake_args.append('-DCMAKE_VERBOSE_MAKEFILE=ON')
 
   return base_cmake_args