Question regarding cross-compiling to SPARCv9 Solaris 10

Hello!
I've been unable to find any information for how to cross-compile Newlib, or a list of supported targets. I am not very experienced with autotools, so I don't really know how to debug this.

Simple things like

<code>
LD=ld.lld CC='clang' CFLAGS='--target=sparc64-solaris' ./configure CROSS_COMPILE="sparc64-sun-solaris" --host=sparc64-sun-solaris --build=x86_64-pc-linux-gnu
</code>

Seem to be failing (this specific one fails by configure emitting a test C file that depends on libc, which obviously fails, since there's no libc for the target present, as that's what I am trying to compile)

Do note that the compiler has no problems compiling freestanding binaries for that target with `-nostdinc -nostd`.

I _guessed_ that Newlib supports SPARC and Solaris since `sparc64-solaris` seems to be listed in the ChangeLog and some of the build files. 

Any help is appreciated,
- Tranquil Ity