Fallback to default paths linux paths if no dpkg-architecture exists

[kkopachev]

Fixes #3103 .

Changes proposed in this pull request:

• When setup run on debian-like OS without dpkg-architecture installed, fallback to default linux guessing

For some reason debian docker image does not include dpkg-architecture, so trying to extract paths from it is pointless. Why don't we fallback to guessing already in place for other linux distros?

[kkopachev]

there is another solution available #3245

[pslacerda]

That if branch happens on linuxes that have an /etc/debian_version and with your change also only when dpkg-architecture is available. However install dpkg-dev on Fedora and run dpkg-architecture correctly shows an correct DEB_HOST_MULTIARCH variable.

So I would remove the check for /etc/debian_version and only test for the presence of dpkg-architecture, will only happen to work on more linuxes, at least Debian based ones and Fedora.

In #3245, the contents of /etc/ld.so.cache are searched because for sure there are linuxes that don't have dpkg-architecture available but has an /etc/ld.so.cache, expectedly with the same binary format. My guess is that if glibc is installed then this cache has the same format, but I'm not completly sure. I didn't called ldconfig -p directly because sometimes localization interfere on the output of commands and ldconfig don't have an option for a safe to parse output.

[kkopachev]

closing in favor of #3245