static_assert is declared in C23 so we can't reuse that identifier:
* Define our own static_assert conditionally;
* Rename "static assert" hacks to _N as we do already in some places
to avoid a conflict.
ChangeLog:
PR ld/32372
* i386-gen.c (static_assert): Define conditionally.
* mips-formats.h (MAPPED_INT): Rename identifier.
(MAPPED_REG): Rename identifier.
(OPTIONAL_MAPPED_REG): Rename identifier.
* s390-opc.c (static_assert): Define conditionally.
