Generate manglings table automatically, which is a part of msvc-support.

1. First, chdir to the directory of this file

clang++ ./prebuild.cc -o prebuild -std=c++2c -I ../../include -O2 -lntdll -fuse-ld=lld -flto=thin
./prebuild $WINDOWS_MSVC_SYSROOT
ninja -C build

if you are in developer environment for vs, you should not pass $WINDOWS_MSVC_SYSROOT.