Bug 1519004 - Use MOZ_LIBAV_FFT on Android if not arm32. r=padenot

"Convolution reverb" of https://padenot.github.io/webaudio-benchmark/ improves
from 8x to 14x on Android/aarch64.

Also, Android/x86 improves from 19x to 21x.

Differential Revision: https://phabricator.services.mozilla.com/D172645

toolkit/moz.configure

@@ -2177,6 +2177,8 @@ with only_when(compile_environment):
 
     @depends(target)
     def libav_fft(target):
+        if target.os == "Android" and target.cpu != "arm":
+            return True
         return target.kernel in ("WINNT", "Darwin") or target.cpu == "x86_64"
 
     set_config("MOZ_LIBAV_FFT", depends(when=libav_fft)(lambda: True))