pkg-infra: munging .la files is not limited to autotools packages

Currently, we're only fixing libtool's .la files for autotools packages,
and even more so, only for those that do not define their own
_INSTALL_STAGING_CMDS.

However, .la files might also be installed by non-autotools packages,
like the NVidia GPU binary blob (libGL.la).

So, move that code into the global build rule, so all packages get their
.la files fixed, whether they be autotools packages or not, and whether
they define their own _INSTALL_STAGING_CMDS or not.

Also print a message.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>