gflags: define NO_THREADS if toolchain doesn't support threads

Fixes:
http://autobuild.buildroot.net/results/a42/a4288ed5050ce0d14e589745bf26c0a95acf645e/

Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gflags/gflags.mk

@@ -11,7 +11,7 @@ GFLAGS_LICENSE = BSD-3c
 GFLAGS_LICENSE_FILES = COPYING.txt
 
 ifeq ($(BR2_TOOLCHAIN_HAS_THREADS),)
-GFLAGS_CONF_OPTS = -DBUILD_gflags_LIB=OFF
+GFLAGS_CONF_OPTS = -DBUILD_gflags_LIB=OFF -DCMAKE_CXX_FLAGS=-DNO_THREADS
 endif
 
 $(eval $(cmake-package))