add '--enable-debug' configure option to build with EMIT_ASN_DEBUG

... which in turn causes all the ASN_DEBUG() to be turned into
fprintf(stderr, ...) statements, once the user application decides
to set 'asn_debug = 1' somewhere in its code.

The next step would be to make _ASN_DECODE_FAILED / _ASN_ENCODE_FAILED
no longer depend on ASN_DEBUG (which it currently does)

configure.ac

@@ -28,6 +28,10 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([char foo;])],
 CFLAGS="$saved_CFLAGS"
 AC_SUBST(SYMBOL_VISIBILITY)
 
+AC_ARG_ENABLE([debug], [AS_HELP_STRING([--enable-debug], [Buld the library with EMIT_ASN_DEBUG enabled])],
+		[build_debug="$enableval"], [build_debug="no"])
+AM_CONDITIONAL(BUILD_DEBUG, test "x$build_debug" = "xyes")
+
 AC_OUTPUT(
         libasn1c.pc
         src/Makefile

include/asn1c/asn_system.h

@@ -21,6 +21,8 @@
 #include <stdarg.h>	/* For va_start */
 #include <stddef.h>	/* for offsetof and ptrdiff_t */
 
+extern int asn_debug;
+
 #ifdef	_WIN32
 
 #include <malloc.h>

src/Makefile.am

@@ -5,6 +5,9 @@ LIBVERSION=1:0:0
 
 AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include/asn1c
 AM_CFLAGS = -fPIC -Wall $(LIBOSMOCORE_CFLAGS)
+if BUILD_DEBUG
+AM_CFLAGS += -DEMIT_ASN_DEBUG=1
+endif
 
 lib_LTLIBRARIES = libasn1c.la
 

src/asn_codecs_prim.c

@@ -6,6 +6,10 @@
 #include <asn_codecs_prim.h>
 #include <errno.h>
 
+#if	EMIT_ASN_DEBUG == 1
+int asn_debug = 0;
+#endif
+
 /*
  * Decode an always-primitive type.
  */