sys-fs/ffmpegfs: remove build system -D_FORTIFY_SOURCE=2

We handle it downstream.
No revbump needed since vanilla Gentoo enables these by default (as of
23.0 profiles)
https://wiki.gentoo.org/wiki/Hardened/Toolchain#Changes

Closes: https://bugs.gentoo.org/936615
Signed-off-by: Lucio Sauer <watermanpaint@posteo.net>

sys-fs/ffmpegfs/ffmpegfs-2.16-r1.ebuild

@@ -40,6 +40,8 @@ PATCHES=(
 
 src_prepare() {
 	default
+	# bug 936615
+	sed 's/-D_FORTIFY_SOURCE=2//' -i Makefile.am || die
 	eautoreconf
 }