Problem building from ARM64

[Carlo B.]

Hello,
I wanted to try to build WINE for ARM64 but I'm having some problems.
The configure script gives me this error message:

"You need clang >= 5.0 to build Wine for arm64."

I understand that probably I have to use clang instead of GCC because
the missing support of __builtin_ms_va_list, but the problem is that
I'm not able to find that anywhere and the most recent one is clang
4.0 into the list of available packages. Where did you get the right
tools? Even the toolchains at developer.arm.com do not include this
feature.

I'm using i686 Debian 9.8.0 multiarch with aarch64-linux-gnu cross compiler.
Perhaps it would be worth to update this thing and its solution also
in the wiki page of the ARM64 port:

https://wiki.winehq.org/ARM64

Sincerely.