event/opdl: fix build using C99 mode

RHEL 7.4 gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)

‘for’ loop initial declarations are only allowed in C99 mode

Fixes: 4236ce9bf5bf ("event/opdl: add OPDL ring infrastructure library")

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>

drivers/event/opdl/Makefile

@@ -7,6 +7,8 @@ include $(RTE_SDK)/mk/rte.vars.mk
 LIB = librte_pmd_opdl_event.a
 
 # build flags
+CFLAGS += -std=c99
+CFLAGS += -D_XOPEN_SOURCE=600
 CFLAGS += -O3
 CFLAGS += $(WERROR_FLAGS)
 # for older GCC versions, allow us to initialize an event using