Build webkit2gtk without JIT/BTI for arm64

BTI enabled WebKit is broken on arm64. MiniBrowser/Epiphany Browser will crash on Apple M2.

(epiphany:25098): epiphany-WARNING **: 12:19:10.808: Web process crashed
[Detaching after vfork from child process 26086]
[Detaching after vfork from child process 26091]
[Thread 0xfffe92fdeaa0 (LWP 26075) exited]

Thread 1 "epiphany" received signal SIGABRT, Aborted.
0x0000ffff192b7dc0 in ?? () from /lib/aarch64-linux-gnu/libc.so.6

/usr/lib/aarch64-linux-gnu/webkitgtk-6.0/MiniBrowser

* (MiniBrowser:38556): WARNING *: 12:49:21.052: WebProcess CRASHED

(MiniBrowser:38556): Gtk-WARNING **: 12:49:21.054: Error embedding AT-SPI socket: GDBus.Error:org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying

Fedora Asahi patches WebKit by using the mbranch-protection=pac-ret only, see:

https://src.fedoraproject.org/rpms/webkitgtk/c/fac6852e5695051ade276ed08835d7baa487bf32?branch=rawhide

If that approach would not be acceptable for the Debian downstream package, can we create one in Bananas?

Example patch would be: https://github.com/reviczky/webkit-bti/commit/e7226117a8d976300e3be0037f999fafde3e7c0f