devtools: fix lib directory in pkg-config test

devtools: fix lib directory in pkg-config test

With Debian and Ubuntu, the default installation path for the 64-bit
libraries is set to e.g. /usr/local/lib/x86_64-linux-gnu/, compared to
/usr/local/lib64 on Fedora and Redhat distributions. This causes issues
when using "pkg-config --define-prefix" since pkg-config assumes the prefix
to be the grandparent of where the .pc file is. On Ubuntu we then get the
cflags include path as being "/path/to/install-root/usr/local/lib/include"
i.e. with an extra "lib" in the path.

This issue only applies for test installs on Ubuntu and similar distros,
and is not a problem for regular installs since the --define-prefix
parameter would not be passed to pkg-config in those cases.

The workaround for this in our test build script is to explicitly make
"lib" the "libdir" setting for the install, overriding the distro-provided
default.

Fixes: 7f80a2102bbb ("devtools: test pkg-config file")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Luca Boccassi <bluca@debian.org>