NetBSD tools/gmp build.sh issues on Solaris-11.4

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

Hello, I'm trying to see if I can build NetBSD on Solaris-11.4 and I'm
having issues with tools/gmp.

I have GCC installed under /opt/gcc/ and by default it generates 64-bit
binaries. However, for some reason, NetBSD tools/gmp defaults to 32-bit
configuration. Unsurprisingly this causes failures later on during the
build.

checking build system type... sparc-sun-solaris2.11
checking host system type... sparc-sun-solaris2.11
...

This really needs to be sparc64-sun-solaris2.11. I set these before
running build.sh:

export HOST_CC=gcc
export HOST_CXX=g++
export PATH=/opt/gcc/bin:/usr/xpg4/bin:/usr/bin:/usr/sbin

Tried setting ABI=64 but it's not that simple, it still fails:
configure: error: ABI=64 is not among the following valid choices: 32

Is there a way to force build.sh ABI and build/host system to be
64-bit when cross-compiling NetBSD?

I'm not sure if gmp configure script is just dumb and does not check if
compiler test outputs 64-bit objects, or if NetBSD build.sh scripts
pass incorrect sparc-sun-solaris2.11 on command line.

Please CC me when replying, as I'm not currently subscribed to
netbsd-users list.

Thanks.