pkgconf: require libosmocore

osmocom/abis/e1_input.h includes osmocom/core/linuxlist.h, therefore
the .pc file(s) need a dependency on libosmocore so that the Cflags
from libosmocore.pc make an appearance on the compiler command line
when using `pkg-config libosmoabis --cflags`.

Committed-by: Max <msuraev@sysmocom.de>
Change-Id: Iacf4ccdb1c2a0e64ac997bda11161b8fe2548725
diff --git a/libosmoabis.pc.in b/libosmoabis.pc.in
index 751149d..da113fc 100644
--- a/libosmoabis.pc.in
+++ b/libosmoabis.pc.in
@@ -8,4 +8,4 @@
 Version: @VERSION@
 Libs: -L${libdir} -losmoabis
 Cflags: -I${includedir}/
-
+Requires: libosmocore