Meson: The default libdir for non system-wide prefix should be 'lib'

[arteymix]

Meson currently uses lib64 when installing with --prefix=$HOME/.local and prefix=/usr/local, but that's an exception for system-wide installation and not a general rule.

I think that lib64 should be checked relatively to the prefix of installation instead.

To be more concise, this is happening on system that have a /usr/lib64 directory (i.e. Fedora) as it is hard-coded in https://github.com/mesonbuild/meson/blob/master/mesonbuild/mesonlib.py#L325

[nirbheek]

The main problem seems to be that our default libdir doesn't take the prefix into account. It will require a bit of refactoring to pass that to default_libdir(), but it is doable.

[ccope]

I just hit the linked issue with libfuse. On Ubuntu 16.04 it's installing the library into /usr/local/lib/x86_64-linux-gnu, but only ld only searches /usr/local/lib.

[nirbheek]

(consolidating libdir detection issues in one place)

Duplicate of #2038