This single object also contains the sr_drivers_init function, that will
always be referenced. That ensures that the drivers object files won't
be optimized out during static linking due to the fact that they are
not referenced directly.
This addresses (parts of) bug #802.
Put the extra libraries into SR_EXTRA_LIBS instead of LIBS.
Create an SR_CHECK_LIBS macro to make that easy. Substitute
SR_EXTRA_LIBS into libsigrok.pc, too.
The "Required.private:" field in pkg-config .pc files is used for
declaring that we need the listed libs (pkg-config packages) for
static linking, but not for dynamic linking.
I.e., the "Required.private:" field should be used for libs which we
use internally in libsigrok, but which we do not "expose" ourselves.
For now all libs are listed as "Required.private:" instead of
"Required:", but this may not be entirely correct and needs to be
checked carefully at some later date.
Guido Trentalancia
Aurelien Jacobs
Daniel Elstner
Uwe Hermann