fix ffmpeg versioning

ffmpeg, extracted from a tarball,
was pulling its version from the parent mxe git directory tree,
so this patch simply removes the invocations of git.

mxe-plugins/notwa/ffmpeg-1-version.patch

@@ -0,0 +1,23 @@
+--- a/ffbuild/version.sh
++++ b/ffbuild/version.sh
+@@ -2,20 +2,6 @@
+ 
+ # Usage: version.sh <ffmpeg-root-dir> <output-version.h> <extra-version>
+ 
+-# check for git short hash
+-if ! test "$revision"; then
+-    if (cd "$1" && grep git RELEASE 2> /dev/null >/dev/null) ; then
+-        revision=$(cd "$1" && git describe --tags --match N 2> /dev/null)
+-    else
+-        revision=$(cd "$1" && git describe --tags --always 2> /dev/null)
+-    fi
+-fi
+-
+-# Shallow Git clones (--depth) do not have the N tag:
+-# use 'git-YYYY-MM-DD-hhhhhhh'.
+-test "$revision" || revision=$(cd "$1" &&
+-  git log -1 --pretty=format:"git-%cd-%h" --date=short 2> /dev/null)
+-
+ # Snapshots from gitweb are in a directory called ffmpeg-hhhhhhh or
+ # ffmpeg-HEAD-hhhhhhh.
+ if [ -z "$revision" ]; then