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

Makefile.inc1

@@ -3322,13 +3322,14 @@ _startup_libs+=	lib/libc_nonshared
 _startup_libs+=	lib/libcxxrt
 _startup_libs+=	lib/libsys
 
-_prereq_libs+=	lib/libgcc_eh lib/libgcc_s
-_startup_libs+=	lib/libgcc_eh lib/libgcc_s
+_prereq_libs+=	lib/libgcc_eh lib/libgcc_s lib/libgcc_s_asneeded
+_startup_libs+=	lib/libgcc_eh lib/libgcc_s lib/libgcc_s_asneeded
 
 lib/libc__L: lib/libsys__L
 lib/libgcc_s__L: lib/libc__L
 lib/libgcc_s__L: lib/libc_nonshared__L
-lib/libcxxrt__L: lib/libgcc_s__L
+lib/libgcc_s_asneeded__L: lib/libgcc_s__L
+lib/libcxxrt__L: lib/libgcc_s_asneeded__L
 lib/libcrypt__L: lib/libmd__L
 
 _prebuild_libs=	${_kerberos5_lib_libasn1} \

lib/Makefile

@@ -61,6 +61,7 @@ SUBDIR=	${SUBDIR_BOOTSTRAP} \
 	libfetch \
 	libgcc_eh \
 	libgcc_s \
+	libgcc_s_asneeded \
 	libgeom \
 	libifconfig \
 	libipsec \

lib/libgcc_s_asneeded/Makefile

@@ -0,0 +1,11 @@
+PACKAGE=	clibs
+SHLIB_NAME=	libgcc_s_asneeded.so.1
+SHLIBDIR?=	/lib
+
+SHLIB_LDSCRIPT=	libgcc_s_asneeded.ldscript
+
+.include <bsd.opts.mk>
+
+LDFLAGS+=	-nodefaultlibs
+
+.include <bsd.lib.mk>

lib/libgcc_s_asneeded/libgcc_s_asneeded.ldscript

@@ -0,0 +1 @@
+INPUT (AS_NEEDED(-lgcc_s))