I have DilOS (illumos based platform) on SPARC64 T5220

gcc 6.4.0 bootstrap with GNU AS + illumos ld

root@bld13:/root# gcc-6 -v
Using built-in specs.
COLLECT_GCC=gcc-6
COLLECT_LTO_WRAPPER=/usr/gcc/6/lib/gcc/sparcv9-sun-solaris2.11/6.4.0/lto-wrapper
Target: sparcv9-sun-solaris2.11
Configured with: ../configure --prefix=/usr/gcc/6 --build=sparcv9-sun-solaris2.11 --bindir=/usr/gcc/6/bin --sbindir=/usr/gcc/6/sbin --libdir=/usr/gcc/6/lib --libexecdir=/usr/gcc/6/lib --infodir=/usr/gcc/6/share/info --mandir=/usr/gcc/6/share/man --target=sparcv9-sun-solaris2.11 --enable-targets=sparc-sun-solaris2.11 --enable-shared --enable-plugins --enable-lto --enable-initfini-array --enable-tls --enable-threads=posix --without-gnu-ld --with-ld=/usr/bin/ld --with-gnu-as --with-as=/usr/bin/gas --enable-languages=c,c++,fortran,go,java,lto,objc --with-system-zlib gcc_cv_ld_as_needed=no --disable-bootstrap
Thread model: posix
gcc version 6.4.0 (GCC) 

i can see core file due to bootstrap:

root@sparc5:/var/cores# pstack core.gcj-dbtool.47078 | c++filt
core 'core.gcj-dbtool.47078' of 47078:  /ws/jenkins/ws/du/components/gcc-6/build/gcc-6-6.4.0/build/sparcv9-sun
 fffffffea61f8bac _lwp_kill (1, 6, 0, fffffffec2402b4d, 0, fffffffec2403e48) + 8
 fffffffea618ef14 raise (0, 0, ffffffff7fff9d70, fffffffec240dfa4, fffffffec25127a8, 0) + 14
 fffffffea616637c abort (5, ffffffff7fff9e60, ffffffffffffffff, 0, 0, ffffffff7fffa9e1) + ac
 fffffffec240dfa4 uw_init_context_1 (ffffffff7fffa5f0, ffffffff7fffb0c0, fffffffe45f3da6c, fffffffe45f3da6c, ffffffff7fff9e60, c00) + 334
 fffffffec240e64c _Unwind_Backtrace (fffffffe45f3d760, ffffffff7fffc128, 0, ffffffff7fffa9e0, ffffffff7fffa5f0, 8000) + 18
 fffffffe45f3da6c _Jv_StackTrace::GetStackTrace() (ffffffff6f741688, 1, 4, fffffffe462efff4, 17c8, ffffffff7fffb170) + 58
 fffffffe45f80d48 java::lang::VMThrowable* java::lang::VMThrowable::fillInStackTrace(java::lang::Throwable*) (0, ffffffff6ed00c60, fffffffe462f029c, fffffffe44d6a56a, 0, fffffffe45f0dfd0) + 2c
 fffffffe46307314 java::lang::Throwable* java::lang::Throwable::fillInStackTrace() (1001d6800, fffffffe47029338, fffffffe462f02e4, fffffffe462f029c, 0, fffffffe45ef81a8) + 4
 fffffffe462f000c java::lang::Throwable::Throwable(java::lang::String*) (1001d6800, 1001d2ae0, fffffffe462f02fc, fffffffe462f02e4, 0, fffffffe45f0dfe8) + 18
 fffffffe462f029c java::lang::Exception::Exception(java::lang::String*) (1001d6800, 1001d2ae0, fffffffe45f79794, fffffffe462f02fc, 0, fffffffe45eeb1b8) + 8
 fffffffe462f02e4 java::lang::ReflectiveOperationException::ReflectiveOperationException(java::lang::String*) (1001d6800, 1001d2ae0, 0, fffffffe45f79794, 38, 1001d6800) + 8
 fffffffe462f02fc java::lang::ClassNotFoundException::ClassNotFoundException(java::lang::String*) (1001d6800, 1001d2ae0, ffffffffffffffff, ffffffff7fffc620, 0, fffffffe47966b88) + 8
 fffffffe45f79794 java::lang::Class* java::lang::Class::forName(java::lang::String*, bool, java::lang::ClassLoader*) (1001d2ae0, 1, 0, 1001ab8a0, 1d, 1001d6800) + f0
 fffffffe46334738 void java::net::URLClassLoader::addURLImpl(java::net::URL*) (1001a9ae0, 10019ca80, 10016ff80, fffffffe47975c38, 1001a9ae0, 1001ab880) + f8
 fffffffe46334cf0 void java::net::URLClassLoader::addURL(java::net::URL*) (1001a9ae0, 10019ca80, 10016ff80, ffffffffffffffff, 1001d2f60, 1001d2f60) + 1c
 fffffffe45f98950 void gnu::gcj::runtime::SystemClassLoader::init() (1001a9ae0, fffffffe473fbae8, 1001abaa0, 10016ef30, 10016edb0, 1001d6e80) + 260
 fffffffe45f325a0 _Jv_CreateJavaVM (0, ffffffff7fffcbf8, 100003b9c, 18, ffffffff7fffc910, ffffffff7fffc920) + 634
 fffffffe45f32b9c _Jv_RunMain(_Jv_VMInitArgs*, java::lang::Class*, char const*, int, char const**, bool) (0, 100108098, 0, 3, ffffffff7fffcbf8, 0) + 1c
 0000000100003da4 main (0, ffffffff7fffcbf8, ffffffff7fffcc18, ffffffffffffffff, 0, 0) + 3c
 0000000100003bf0 _start_crt (3, ffffffff7fffcbf8, ffffffff6f61c5e4, 0, 0, 0) + 6c
 0000000100003b74 _start (0, 0, 0, 0, 0, 0) + 14

gcc-6 build can be finished successfully.
it is similar core file with Unwind issue what i have with gcc-go, but will file another issue with details