x11/libICE: Fix C++ interoperability error due to static_assert define (+)

Backport critical fix from upstream.

Upstream commit 0269c687 added a static_assert helper
that gets defined to blank if left undefined by assert.h.
As this is not a macro in other languages that use this header,
this can lead to a compile-time error.

See also: https://gitlab.freedesktop.org/xorg/lib/libice/-/commit/e176b676cff17948d68299c00dddefe41638c752

Pointy hat to: manu (for skipped exp-run)
Approved by: portmgr blanket