libgcc_s: add libgcc_s_asneeded.so wrapper for gcc 16

GCC 16[0][1] now requires a wrapper lib to handle
`--push-state --as-needed -lgcc_s --pop-state` logic[1]
for `gcc` invocations. `g++` will stil

libgcc_s: add libgcc_s_asneeded.so wrapper for gcc 16

GCC 16[0][1] now requires a wrapper lib to handle
`--push-state --as-needed -lgcc_s --pop-state` logic[1]
for `gcc` invocations. `g++` will still unconditionally
use `-lgcc_s`.

This fixes buildworld with gcc16.

[0] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=8a99fdb70493df1294b53406913e5ea1fc971c13
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123396

Reviewed by: jhb
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D59511

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