configure/help: consistently use "autodetect"

configure

@@ -133,9 +133,9 @@ Component options:
   --disable-postproc       disable libpostproc build
   --disable-avfilter       disable libavfilter build
   --enable-avresample      enable libavresample build [no]
-  --disable-pthreads       disable pthreads [auto]
-  --disable-w32threads     disable Win32 threads [auto]
-  --disable-os2threads     disable OS/2 threads [auto]
+  --disable-pthreads       disable pthreads [autodetect]
+  --disable-w32threads     disable Win32 threads [autodetect]
+  --disable-os2threads     disable OS/2 threads [autodetect]
   --disable-network        disable network support [no]
   --disable-dct            disable DCT code
   --disable-dwt            disable DWT code
@@ -255,10 +255,10 @@ External library support:
   --enable-libx264         enable H.264 encoding via x264 [no]
   --enable-libx265         enable HEVC encoding via x265 [no]
   --enable-libxavs         enable AVS encoding via xavs [no]
-  --enable-libxcb          enable X11 grabbing using XCB [auto]
-  --enable-libxcb-shm      enable X11 grabbing shm communication [auto]
-  --enable-libxcb-xfixes   enable X11 grabbing mouse rendering [auto]
-  --enable-libxcb-shape    enable X11 grabbing shape rendering [auto]
+  --enable-libxcb          enable X11 grabbing using XCB [autodetect]
+  --enable-libxcb-shm      enable X11 grabbing shm communication [autodetect]
+  --enable-libxcb-xfixes   enable X11 grabbing mouse rendering [autodetect]
+  --enable-libxcb-shape    enable X11 grabbing shape rendering [autodetect]
   --enable-libxvid         enable Xvid encoding via xvidcore,
                            native MPEG-4/Xvid encoder exists [no]
   --enable-libzmq          enable message passing via libzmq [no]