configure: Do not unconditionally add -D_POSIX_C_SOURCE to CPPFLAGS.

Adding _POSIX_C_SOURCE to CPPFLAGS globally produces all sorts of problems
since it causes certain system functions to be hidden on some (BSD) systems.
The solution is to only add the flag on systems that really require it, i.e.
glibc-based ones.

This change makes BSD systems compile out-of-the-box without the need for
adding specific flags manually.  It also allows dropping a number of flags
set manually on a file-per-file basis, but were only present to work around
breakage introduced by the presence of _POSIX_C_SOURCE.

Also add _XOPEN_SOURCE to CPPFLAGS for glibc systems.  We use XSI extensions
in several places already, so it is preferable to define it globally instead
of littering source files with individual #defines only needed for glibc.

configure

@@ -1664,7 +1664,7 @@ LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
 
 CC_O='-o $@'
 
-host_cflags='-D_ISOC99_SOURCE -D_POSIX_C_SOURCE=200112 -O3 -g -Wall'
+host_cflags='-D_ISOC99_SOURCE -O3 -g -Wall'
 host_libs='-lm'
 
 target_path='$(CURDIR)'
@@ -2316,7 +2316,7 @@ if test "$?" != 0; then
     die "C compiler test failed."
 fi
 
-add_cppflags -D_ISOC99_SOURCE -D_POSIX_C_SOURCE=200112
+add_cppflags -D_ISOC99_SOURCE
 check_cflags -std=c99
 check_cc -D_FILE_OFFSET_BITS=64 <<EOF && add_cppflags -D_FILE_OFFSET_BITS=64
 #include <stdlib.h>
@@ -2364,7 +2364,6 @@ case $target_os in
         disable symver
         oss_indev_extralibs="-lossaudio"
         oss_outdev_extralibs="-lossaudio"
-        add_cppflags -D_XOPEN_SOURCE=600
         ;;
     openbsd)
         enable malloc_aligned
@@ -2457,6 +2456,7 @@ case $target_os in
         enable dos_paths
         ;;
     linux)
+        add_cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
         enable dv1394
         ;;
     irix*)

doc/general.texi

@@ -785,14 +785,6 @@ to configure.
 BSD make will not build Libav, you need to install and use GNU Make
 (@file{gmake}).
 
-@subsubsection FreeBSD, DragonFly BSD
-
-These systems will not compile out-of-the-box due to broken system headers.
-Passing @code{--extra-cflags=-D__BSD_VISIBLE} to configure will work
-around the problem. This may have unexpected sideeffects, so use it at
-your own risk. If you care about FreeBSD, please make an attempt at
-getting the system headers fixed.
-
 @subsection (Open)Solaris
 
 GNU Make is required to build Libav, so you have to invoke (@file{gmake}),

ffmpeg.c

@@ -19,9 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-/* needed for usleep() */
-#define _XOPEN_SOURCE 600
-
 #include "config.h"
 #include <ctype.h>
 #include <string.h>

ffplay.c

@@ -19,8 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#define _XOPEN_SOURCE 600
-
 #include "config.h"
 #include <inttypes.h>
 #include <math.h>

ffserver.c

@@ -19,8 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#define _XOPEN_SOURCE 600
-
 #include "config.h"
 #if !HAVE_CLOSESOCKET
 #define closesocket close

libavcodec/libxvidff.c

@@ -25,9 +25,6 @@
  * @author Adam Thayer (krevnik@comcast.net)
  */
 
-/* needed for mkstemp() */
-#define _XOPEN_SOURCE 600
-
 #include <xvid.h>
 #include <unistd.h>
 #include "avcodec.h"

libavdevice/bktr.c

@@ -24,10 +24,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#define _BSD_SOURCE 1
-#define _NETBSD_SOURCE
-#define _XOPEN_SOURCE 600
-
 #include "libavformat/avformat.h"
 #if HAVE_DEV_BKTR_IOCTL_METEOR_H && HAVE_DEV_BKTR_IOCTL_BT848_H
 # include <dev/bktr/ioctl_meteor.h>

libavdevice/x11grab.c

@@ -35,8 +35,6 @@
  * and Edouard Gomez <ed.gomez@free.fr>.
  */
 
-#define _XOPEN_SOURCE 600
-
 #include "config.h"
 #include "libavformat/avformat.h"
 #include <time.h>

libavformat/applehttp.c

@@ -25,7 +25,6 @@
  * http://tools.ietf.org/html/draft-pantos-http-live-streaming
  */
 
-#define _XOPEN_SOURCE 600
 #include "libavutil/avstring.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/opt.h"

libavformat/applehttpproto.c

@@ -25,7 +25,6 @@
  * http://tools.ietf.org/html/draft-pantos-http-live-streaming
  */
 
-#define _XOPEN_SOURCE 600
 #include "libavutil/avstring.h"
 #include "avformat.h"
 #include "internal.h"