tools/rtla: Build with EXTRA_{C,LD}FLAGS

To allow for distributions and other builders to apply hardening
policy and other customisation, append EXTRA_CFLAGS and EXTRA_LDFLAGS
to the corresponding variables.

Link: https://lore.kernel.org/linux-trace-devel/YtLBshz0nMQ7530H@decadent.org.uk



Signed-off-by: Ben Hutchings <benh@debian.org>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>