trace-cmd: remove the compile fix patch

And instead override TARGET_CFLAGS to set _GNU_SOURCE accordingly since
this is the upstream maintainer solution.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37152 3c298f89-4303-0410-b956-a3cf2f4a3e73