Add libosmo-rspro.pc.in for pkg-config integration

Change-Id: Ic8bbf27bdb5ce7c810ede307a35ad4dc10338912
diff --git a/configure.ac b/configure.ac
index 7281196..1d2ccc2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -129,6 +129,7 @@
 
 AC_OUTPUT(
 	Makefile
+	libosmo-rspro.pc
 	doc/Makefile
 	doc/manuals/Makefile
 	src/Makefile