Re-add the 'regen' targets lost in the automake transition

This might need a lot of cleanup for out-of-source-tree builds and the
like, but let's not spend time on this now.  The old Makefile also
didn't support that.  But loosing the ability to regenerate the C source
is not an option either.
diff --git a/src/hnbap/Makefile.am b/src/hnbap/Makefile.am
index 920b8fc..a9e8163 100644
--- a/src/hnbap/Makefile.am
+++ b/src/hnbap/Makefile.am
@@ -238,3 +238,10 @@
 libosmo_asn1_hnbap_a_SOURCES=$(ASN_MODULE_SOURCES)
 include_HEADERS = $(ASN_MODULE_INC)
 libosmo_asn1_hnbap_a_LIBADD=$(ASN1C_LDADD)
+
+regen: regenerate-from-asn1-source
+
+regenerate-from-asn1-source:
+	asn1c -gen-PER -fnative-types ../../asn1/hnbap/HNBAP-CommonDataTypes.asn ../../asn1/hnbap/HNBAP-Constants.asn ../../asn1/hnbap/HNBAP-IEs.asn ../../asn1/hnbap/HNBAP-PDU.asn
+#	remove the local copy of the runtime code
+	@rm ANY.* BOOLEAN.* INTEGER.* NativeEnumerated.* NativeInteger.* OBJECT_IDENTIFIER.* asn_* OCTET_STRING.* converter-sample.c per_* xer_* constr* der_* ber_* BIT_STRING.*