ffmpeg: use gmp for rtmp(e) (#427202)

pkgs/development/libraries/ffmpeg/generic.nix

@@ -87,6 +87,7 @@
   withFrei0r ? withFullDeps && withGPL, # frei0r video filtering
   withFribidi ? withHeadlessDeps, # Needed for drawtext filter
   withGme ? withFullDeps, # Game Music Emulator
+  withGmp ? withHeadlessDeps && withVersion3, # rtmp(t)e support
   withGnutls ? withHeadlessDeps,
   withGsm ? withFullDeps, # GSM de/encoder
   withHarfbuzz ? withHeadlessDeps && lib.versionAtLeast version "6.1", # Needed for drawtext filter
@@ -124,7 +125,7 @@
   withQuirc ? withFullDeps && lib.versionAtLeast version "7", # QR decoding
   withRav1e ? withFullDeps, # AV1 encoder (focused on speed and safety)
   withRist ? withHeadlessDeps, # Reliable Internet Stream Transport (RIST) protocol
-  withRtmp ? withFullDeps, # RTMP[E] support
+  withRtmp ? false, # RTMP[E] support via librtmp
   withRubberband ? withFullDeps && withGPL && !stdenv.hostPlatform.isFreeBSD, # Rubberband filter
   withSamba ? withFullDeps && !stdenv.hostPlatform.isDarwin && withGPLv3, # Samba protocol
   withSdl2 ? withSmallDeps,
@@ -259,6 +260,7 @@
   frei0r,
   fribidi,
   game-music-emu,
+  gmp,
   gnutls,
   gsm,
   harfbuzz,
@@ -650,6 +652,7 @@ stdenv.mkDerivation (
       (enableFeature withFrei0r "frei0r")
       (enableFeature withFribidi "libfribidi")
       (enableFeature withGme "libgme")
+      (enableFeature withGmp "gmp")
       (enableFeature withGnutls "gnutls")
       (enableFeature withGsm "libgsm")
     ]
@@ -874,6 +877,7 @@ stdenv.mkDerivation (
       ++ optionals withFrei0r [ frei0r ]
       ++ optionals withFribidi [ fribidi ]
       ++ optionals withGme [ game-music-emu ]
+      ++ optionals withGmp [ gmp ]
       ++ optionals withGnutls [ gnutls ]
       ++ optionals withGsm [ gsm ]
       ++ optionals withHarfbuzz [ harfbuzz ]