The new HAVE_LD_AS_NEEDED support doesn't seem to work on Solaris 9 and 10:

(botcazou@ob) /nile.build/botcazou/gcc-head/sparc-sun-solaris2.10 $ cat t.c
int main (void) { return 0; }
(botcazou@ob) /nile.build/botcazou/gcc-head/sparc-sun-solaris2.10 $ gcc/xgcc -Bgcc -o t t.c     
(botcazou@ob) /nile.build/botcazou/gcc-head/sparc-sun-solaris2.10 $ ldd t
        libgcc_s.so.1 =>         /usr/local/gnatpro/6.4.2/lib/libgcc_s.so.1
        libc.so.1 =>     /lib/libc.so.1
        libm.so.2 =>     /lib/libm.so.2
        /platform/SUNW,Sun-Fire-V240/lib/libc_psr.so.1

The dependency on libgcc_s.so.1 for a dummy program is new.  This is critical because this breaks bootstrap:

make[1]: *** [all] Error 2
make[1]: Leaving directory `/nfs/nile/nile.build/botcazou/gcc-head/sparc-sun-solaris2.10/sparc-sun-solaris2.10/libquadmath'
make: *** [all-target-libquadmath] Error 2

configure:3386: checking whether the C compiler works
configure:3395: ./a.out
ld.so.1: ./a.out: fatal: /nile.build/botcazou/gcc-head/sparc-sun-solaris2.10/./gcc/libgcc_s.so.1: wrong ELF class: ELFCLASS32
/nile.build/botcazou/gcc-head/src/libquadmath/configure: line 1: 10727 Killed                  ./$ac_file
configure:3399: $? = 137
configure:3406: error: in `/nile.build/botcazou/gcc-head/sparc-sun-solaris2.10/sparc-sun-solaris2.10/sparcv9/libquadmath':
configure:3410: error: cannot run C compiled programs.
If you meant to cross compile, use `--host'.
See `config.log' for more details.