Ensure llvm builds don't use libc++ (#554)

* Ensure winarm64 builds don't use libc++

* Update build-win.py

* Update build-win.py

Co-authored-by: Brandon Gavino <[email protected]>

Author: brgavino

scripts/build-win.py

@@ -32,14 +32,21 @@
     'enable_libaom=true',
     'rtc_build_examples=false',
     'treat_warnings_as_errors=false',
-]
+    ]
 
 
 def gngen(arch, ssl_root, msdk_root, quic_root, scheme, tests):
     gn_args = list(GN_ARGS)
     gn_args.append('target_cpu="%s"' % arch)
-    if arch != 'arm64':
+    using_llvm = False
+    if arch == 'arm64':
+        using_llvm = True
+    if  not using_llvm:
         gn_args.append('is_clang=false')
+    else:
+        gn_args.append('libcxx_abi_unstable=false')
+        gn_args.append('use_custom_libcxx_for_host=false')
+        gn_args.append('use_custom_libcxx=false')
     if scheme == 'release':
         gn_args.append('is_debug=false')
     else: