Use gcc --sysroot in rap stage3 post glibc install

[bartoldeman]

Since glibc now has non-prefixed filenames in
$EPREFIX/usr/lib64/libc.so, it picks up non-prefixed /lib64/libc.so.6 from stage2 gcc, unless we replace its -I, -L, and -B options by --sysroot. Then it will look at the same places as the future stage3 gcc.

This avoids issues building binutils, which can't find dlopen in older /lib64/libc.so.6, since dlopen used to be in libdl instead.

The whole logic no longer tests for compiler == gcc, since clang is only used for non-rap on MacOS.

[chewi]

Looks great, thanks! Just one minor thing, gcc documents the --sysroot option as being --sysroot=dir so please add the =. That's how I've always used it.

Now I understand why I didn't see this issue when testing. I was bootstrapping on top of Gentoo, and my host libc matched the prefix libc, so it didn't break. When I tested cross-compiling, I didn't use bootstrap-prefix.sh, but used cross-boss, which already adds --sysroot to the flags.

[bartoldeman]

Thanks for the feedback, I added the =. Funnily enough GCC docs have --sysroot= but --isysroot without the =.

There's another issue in the bootstrap much later with dev-libs/libgcrypt when bootstrapping on a CentOS7 kernel, which can be fixed by setting the -getentropy USE flag. I'm waiting for my bootstrap to finish, and will then submit a PR about that too.

[zigford]

With this patch, I was finally able to run gentoo-prefix on RedHat 8. Thanks

[bartoldeman]

I submitted the getentropy fix as
gentoo/gentoo#29906

[APN-Pucky]

Debian 11 works with this too.

[thesamesam]

Many thanks for this!