atf: ignore warnings emitted by newer compilers

This commit is needed in order to get arm-trusted-firmware to build
with recent gcc and binutils.

src/platform/kevin/atf/default.nix

@@ -53,6 +53,12 @@ in
   # -F3 is needed in order to force the backport patches below to apply to an older atf
   patchFlags = [ "-p1" "-F3" ];
 
+  # "error: ignoring attribute ... because it conflicts with previous ..."
+  NIX_CFLAGS_COMPILE = "-Wno-attributes";
+
+  # needed with binutils >= 2.39: https://developer.trustedfirmware.org/T996#11847
+  NIX_CFLAGS_LINK = "-Wl,--no-warn-rwx-segment";
+
   patches = [
 
     # backport from atf-2.3: "rockchip: Update BL31_BASE to 0x40000"