[Bug c/90653] --with-build-sysroot= not honored for ./configure C compiler checks.

[kallisti5 at unixzen dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90653

--- Comment #4 from Alexander von Gluck <kallisti5 at unixzen dot com> ---
ok, this one got kinda long. I've discovered the "how".

gcc7 calling the linker using a --sysroot:

/work/generated.ppc/objects/haiku/ppc/packaging/repositories/HaikuPortsCross-build/sys-devel/gcc_bootstrap/work-8.3.0_2019_05_24/boot/cross-sysroot/ppc/boot/system/develop/lib/crtn.o


gcc8 calling the linker using a --sysroot:

crtn.o


What would remove the sysroot prefix from the STARTFILES?