Fix ldconfig for GCC installs

[alexezeder]

Fixes #75

Without this fix I have to have a derived image with:

RUN rm /etc/ld.so.conf.d/local-lib64.conf && sed -i '1s/^/\/usr\/local\/lib64\n/' /etc/ld.so.conf && ldconfig

which gives me the correct order of libstdc++:

$ ldconfig -p | grep libstdc++
        libstdc++.so.6 (libc6,AArch64) => /usr/local/lib64/libstdc++.so.6
        libstdc++.so.6 (libc6,AArch64) => /usr/lib/aarch64-linux-gnu/libstdc++.so.6
        libstdc++.so (libc6,AArch64) => /usr/local/lib64/libstdc++.so

[tianon]

Whoa, great catch -- however, I don't think we need to get quite this complicated. It should be enough for us to rename local-lib64.conf to something that sorts above aarch64 (and any other architecture string), so this should be enough:

Suggested change

	sed -i '1s/^/\/usr\/local\/lib64\n/' /etc/ld.so.conf; \
	echo '/usr/local/lib64' > /etc/ld.so.conf.d/000-local-lib64.conf; \

(This also made me realize this is probably broken completely on 32bit architectures like arm32v7, but I think that's something we should solve separately. 😄 32bit are not "broken" but are also not fine since arm- sorts above the filename that includes /usr/local/lib so we probably should get explicit there too for the same reason 😄)

[tianon]

Aha, https://bugs.debian.org/685706 is where I'd seen this before and couldn't find. 😄

[alexezeder]

Oh, you did this work for me 😉
Anyway it looks fine, hope there won't be any 000... architectures created soon...