kbuild: avoid static_assert for genksyms

kbuild: avoid static_assert for genksyms

genksyms does not know or care about the _Static_assert() built-in, and
sometimes falls back to ignoring the later symbols, which causes
undefined behavior such as

  WARNING: modpost: EXPORT symbol "ethtool_set_ethtool_phy_ops" [vmlinux] version generation failed, symbol will not be versioned.
  ld: net/ethtool/common.o: relocation R_AARCH64_ABS32 against `__crc_ethtool_set_ethtool_phy_ops' can not be used when making a shared object
  net/ethtool/common.o:(_ftrace_annotated_branch+0x0): dangerous relocation: unsupported relocation

Redefine static_assert for genksyms to avoid that.

Link: https://lkml.kernel.org/r/20201203230955.1482058-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>