[config] Many updates to configuration and feature checks

- Added custom checks for libraries and pkgconfig modules that test library
 presence with additional checks for use of headers and functions with
 given options.  Also support correct additional feature library checks
 using provided flags.
- Added custom enable/disable feature macros to simplify their use.
- Use custom CFLAGS and LIBS variables for Makefiles to simplify maintenance.
- Update many feature checks from platform to function.
- Streamline many function checks.
- Correctly check gnutls, gcrypt and gpg-error libraries.
- Fix chromecast and spotify config and compile on FreeBSD
- Added inotify, signalfd and kqueue, and byte swap checks.
- Many clarifications of error messages.
- Correct json-c checks to properly use supplied CFLAGS.
- Correct many quoting inconsistencies
- Use __DATE__ in place of BUILDDATE
- Use full path for gperf and antlr3
- Remove unnecessary CFLAGS
- Added tests for pthread_setname_np parameters
- Added tests for clock_gettime and timer_settime
- Added tests for time.h
- Test if pthread, dl and rt libs are required/available.
- Updated checks for libunistring

src/httpd.c

@@ -39,8 +39,7 @@
 #include <stdint.h>
 #include <inttypes.h>
 
-#if defined(HAVE_SYS_EVENTFD_H) && defined(HAVE_EVENTFD)
-# define USE_EVENTFD
+#ifdef HAVE_EVENTFD
 # include <sys/eventfd.h>
 #endif
 #include <event2/event.h>
@@ -133,7 +132,7 @@ static const struct content_type_map ext2ctype[] =
 
 struct event_base *evbase_httpd;
 
-#ifdef USE_EVENTFD
+#ifdef HAVE_EVENTFD
 static int exit_efd;
 #else
 static int exit_pipe[2];
@@ -1453,7 +1452,7 @@ httpd_init(void)
 
   streaming_init();
 
-#ifdef USE_EVENTFD
+#ifdef HAVE_EVENTFD
   exit_efd = eventfd(0, EFD_CLOEXEC);
   if (exit_efd < 0)
     {
@@ -1477,7 +1476,7 @@ httpd_init(void)
     }
 
   exitev = event_new(evbase_httpd, exit_pipe[0], EV_READ, exit_cb, NULL);
-#endif /* USE_EVENTFD */
+#endif /* HAVE_EVENTFD */
   if (!exitev)
     {
       DPRINTF(E_FATAL, L_HTTPD, "Could not create exit event\n");
@@ -1549,7 +1548,7 @@ httpd_init(void)
  bind_fail:
   evhttp_free(evhttpd);
  event_fail:
-#ifdef USE_EVENTFD
+#ifdef HAVE_EVENTFD
   close(exit_efd);
 #else
   close(exit_pipe[0]);
@@ -1574,7 +1573,7 @@ httpd_deinit(void)
 {
   int ret;
 
-#ifdef USE_EVENTFD
+#ifdef HAVE_EVENTFD
   ret = eventfd_write(exit_efd, 1);
   if (ret < 0)
     {
@@ -1607,7 +1606,7 @@ httpd_deinit(void)
   dacp_deinit();
   daap_deinit();
 
-#ifdef USE_EVENTFD
+#ifdef HAVE_EVENTFD
   close(exit_efd);
 #else
   close(exit_pipe[0]);