build: check for existence of execinfo.h

GLIBC is not necessarily the only library that provides execinfo.
With libexecinfo execinfo can be used also in other Libraries.
The patch lets the configure check the existence of the header
and the libexecinfo Library and uses them if avaible.

(also fixes compilation if execinfo is not avaible)

configure.ac

@@ -86,6 +86,9 @@ AC_DEFINE_UNQUOTED(CONFIGDIR, "/etc/iwd", [Configuration directory])
 
 AC_CHECK_HEADERS(linux/types.h linux/if_alg.h)
 
+AC_CHECK_HEADERS_ONCE(execinfo.h)
+AC_CHECK_LIB(execinfo, backtrace)
+
 if (test "${enable_client}" != "no"); then
 	AC_CHECK_HEADERS(readline/readline.h, enable_readline=yes,
 			AC_MSG_ERROR(readline header files are required))

plugins/ofono.c

@@ -653,7 +653,9 @@ static void parse_modem(const char *path, struct l_dbus_message_iter *props)
 		 * has been seen to happen.
 		 */
 		l_error("modem %s already found", path);
+#ifdef HAVE_EXECINFO_H
 		__iwd_backtrace_print(2);
+#endif
 		exit(1);
 	}
 

src/backtrace.c

@@ -27,7 +27,7 @@
 #define _GNU_SOURCE
 #include <features.h>
 
-#ifdef __GLIBC__
+#ifdef HAVE_EXECINFO_H
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>