conf: allow wildcard patterns in include directive

Use glob() to match and read multiple configuration files with one
include directive.

chrony.texi.in

@@ -1668,12 +1668,15 @@ hwclockfile /etc/adjtime
 @c {{{ include
 @node include directive
 @subsection include
-The @code{include} directive includes a specified configuration file.
-This is useful when maintaining configuration on multiple hosts to
-keep the differences in a separate file.
+The @code{include} directive includes a specified configuration file or
+multiple configuration files when a wildcard pattern is specified.  This can be
+useful when maintaining configuration on multiple hosts to keep the differences
+in separate files.
+
+An example of the command is
 
 @example
-include @SYSCONFDIR@/chrony/local.conf
+include @SYSCONFDIR@/chrony.d/*.conf
 @end example
 @c }}}
 @c {{{ initstepslew

conf.c

@@ -1236,8 +1236,20 @@ parse_tempcomp(char *line)
 static void
 parse_include(char *line)
 {
+  glob_t gl;
+  size_t i;
+
   check_number_of_args(line, 1);
-  CNF_ReadFile(line);
+
+  if (glob(line, 0, NULL, &gl)) {
+    DEBUG_LOG(LOGF_Configure, "glob of %s failed", line);
+    return;
+  }
+
+  for (i = 0; i < gl.gl_pathc; i++)
+    CNF_ReadFile(gl.gl_pathv[i]);
+
+  globfree(&gl);
 }
 
 /* ================================================== */

sysincl.h

@@ -39,6 +39,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <float.h>
+#include <glob.h>
 #if !defined(__FreeBSD__) && !defined(MACOSX)
 #include <malloc.h>
 #endif