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: Ibf21cfd2ea3f3d0def3c18374118c4cb03a45e05

.gitignore

@@ -54,3 +54,4 @@ src/osmo-gapk
 /compile
 .dirstamp
 
+contrib/gapk.spec

configure.ac

@@ -115,4 +115,4 @@ AC_TYPE_UINT8_T
 AC_FUNC_MALLOC
 AC_CHECK_FUNCS([memset])
 
-AC_OUTPUT
+AC_OUTPUT([contrib/gapk.spec])

contrib/gapk.spec.in

@@ -12,15 +12,12 @@
 # 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/
-#
-
 %define with_amr 1
 %define with_gsmhr 1
 %define sover 0
 
 Name:           gapk
-Version:        0.4.79
+Version:        @VERSION@
 Release:        0
 Summary:        GSM Audio Pocket Knife
 License:        GPL-3.0-only