contrib: integrate RPM spec

Remove OpenSUSE bug report link, set version to @VERSION@, make it build with CentOS 8 etc.

Related: OS#4550
Change-Id: Ic075dd5a53cc76cf1b6aeca5c31db495882db915

.gitignore

@@ -21,3 +21,5 @@ libasn1c.pc
 *.la
 .deps
 .libs
+
+contrib/libasn1c.spec

configure.ac

@@ -75,4 +75,5 @@ AC_OUTPUT(
         src/Makefile
         include/Makefile
         include/asn1c/Makefile
-        Makefile)
+        Makefile
+        contrib/libasn1c.spec)

contrib/libasn1c.spec.in

@@ -12,12 +12,8 @@
 # license that conforms to the Open Source Definition (Version 1.9)
 # published by the Open Source Initiative.
 
-# Please submit bugfixes or comments via http://bugs.opensuse.org/
-#
-
-
 Name:           libasn1c
-Version:        0.9.32.0
+Version:        @VERSION@
 Release:        0
 Summary:        Osmocon ASN.1 decoder and encoder library
 License:        BSD-2-Clause