doc/indevs: mention required configure options

For x11grab, libcdio, and libdc1394 input devices.
Signed-off-by: Lou Logan <lou@lrcd.com>

doc/indevs.texi

@@ -488,7 +488,8 @@ ffplay -f lavfi "movie=test.avi[out0];amovie=test.wav[out1]"
 Audio-CD input device based on cdio.
 
 To enable this input device during configuration you need libcdio
-installed on your system.
+installed on your system. Requires the configure option
+@code{--enable-libcdio}.
 
 This device allows playing and grabbing from an Audio-CD.
 
@@ -502,6 +503,8 @@ ffmpeg -f libcdio -i /dev/sr0 cd.wav
 
 IIDC1394 input device, based on libdc1394 and libraw1394.
 
+Requires the configure option @code{--enable-libdc1394}.
+
 @section openal
 
 The OpenAL input device provides audio capture on all systems with a
@@ -830,6 +833,9 @@ other filename will be interpreted as device number 0.
 
 X11 video input device.
 
+Depends on X11, Xext, and Xfixes. Requires the configure option
+@code{--enable-x11grab}.
+
 This device allows one to capture a region of an X11 display.
 
 The filename passed as input has the syntax: