avfilter: Add missing emms_c when needed

Arch specific calls should have an emms_c following to keep the cpu
state consistent.

Reported-By: wm4
CC: libav-stable@libav.org
(cherry picked from commit e995cf1bccc6e91bbaa6a8771e23fb3ab259c110)
matroskaenc: allow override of "writing application" tag

Signed-off-by: Tim Walker <tdskywalker@gmail.com>

CC: libav-stable@libav.org
(cherry picked from commit 0092c1dd8dac2d9e185b58503b447a0d3fb5230d)
movenc: allow override of "writing application" tag

Signed-off-by: Tim Walker <tdskywalker@gmail.com>

CC: libav-stable@libav.org
(cherry picked from commit 565e0c6d866ce08d4b06427456d3d1f4fd856e9c)