sysstat: fix passing CFLAGS to make

SYSSTAT_MAKE_OPT is a string used to pass options to make, '+=' operator
doesn't have any special meaning inside it, so CFLAGS+=... is passed to
shell, overwriting previous CFLAGS value.

Replace CFLAGS+="..." with CFLAGS="$(TARGET_CFLAGS) ...".

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/sysstat/sysstat.mk

@@ -14,7 +14,7 @@ SYSSTAT_LICENSE_FILES = COPYING
 
 ifeq ($(BR2_NEEDS_GETTEXT_IF_LOCALE),y)
 SYSSTAT_DEPENDENCIES += gettext
-SYSSTAT_MAKE_OPT += CFLAGS+=-lintl
+SYSSTAT_MAKE_OPT += CFLAGS="$(TARGET_CFLAGS) -lintl"
 endif
 
 # The isag tool is a post processing script that depends on tcl/tk