Also only update config.sh when it changed to avoid spurious rebuilds.

The files are no longer generated by configure, so they should not
be removed by the distclean target any longer.

We currently only have exported data symbols within libavcodec, but
the concept is easy to extend to other libraries if necessary.
The attribute declaration needs to be in a private header though,
since we can't use CONFIG_SHARED in public installed headers.
Signed-off-by: Martin Storsjö <martin@martin.st>

Also employ this mechanism to pass $libdir to the runtime library search
path if rpath is enabled. This fixes underlinking of some test binaries
on some systems.

The .version files are only relevant during an actual build.

None of them are specific to the YASM assembler.

Previously, all link-time dependencies were added for all libraries,
resulting in bogus link-time dependencies since not all dependencies
are shared across libraries. Also, in some cases like libavutil, not
all dependencies were taken into account, resulting in some cases of
underlinking.

To address all this mess a machinery is added for tracking which
dependency belongs to which library component and then leveraged
to determine correct dependencies for all individual libraries.

The (required) version numbers disappeared after edb43487.

This moves work from the configure to the Make stage where it can
be parallelized and ensures that pkgconfig files are updated when
library versions change.

Bug-Id: 449

This moves work from the configure to the Make stage where it can
be parallelized and ensures that shared libraries are built with
the right version number in the filename.

This unclutters the top-level directory and groups related files together.