[third_party/ffmpeg] merge some old changes to BUILD.gn

BUILD.gn and other files for ffmpeg have been rebuilt from a recent
version from Chromium. A couple of important changes were lost and
are restored here.

fxr/610499: [build] Explicitly include "novariant" variant
fxr/508076: [build] Always optimize the build for speed

Test: build issue
Change-Id: Id84007ad4279ef5fec50b178143e1c33edb5a8ac
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/ffmpeg/+/746922
Reviewed-by: Nathan Mulcahey <nmulcahey@google.com>
Reviewed-by: Gulfem Savrun Yeniceri <gulfem@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index bf425c7..a45fbcd 100755
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -185,19 +185,14 @@
     ":ffmpegsumo_warnings",
   ]
 
-  # Since we are not often debugging FFmpeg, and performance is
-  # unacceptable without optimization, freeze the optimizations to -O2.
-  # If someone really wants -O1 , they can change these in their checkout.
-  # If you want -O0, see the Gotchas in README.fuchsia for why that
-  # won't work.
+  # Since we are not often debugging FFmpeg, and performance is unacceptable
+  # without optimization, we always optimize for speed.
   #
   # In addition to the above reasons, /Od optimization won't remove symbols
   # that are under "if (0)" style sections.  Which lead to link time errors
   # when for example it tries to link an ARM symbol on X86.
-  if (is_debug) {
-    configs -= [ "//build/config:debug" ]
-    configs += [ "//build/config:release" ]
-  }
+  configs -= [ "//build/config:default_optimize" ]
+  configs += [ "//build/config:optimize_speed" ]
 
   # Make all symbols visible.
   configs -= [ "//build/config:symbol_visibility_hidden" ]
@@ -240,7 +235,11 @@
 
 group("ffmpeg_variants") {
   deps = []
-  foreach(variant, select_variant) {
+  _variants = select_variant
+  if (select_variant != []) {
+    _variants += ["novariant"]
+  }
+  foreach(variant, _variants) {
     deps += [ ":ffmpeg(${toolchain_variant.base}-${variant}-shared)" ]
   }
-}
+}
\ No newline at end of file