package/ntpsec: fix host building

The following build failure on xtensa:

Waf: Entering directory `/home/buildroot/instance-0/output-1/build/ntpsec-1.2.3/build/host'
[1/2] Processing ntpd/ntp_parser.y
[2/2] Compiling build/host/ntpd/ntp_parser.tab.c
gcc: error: unrecognized command-line option '-mlongcalls'
gcc: error: unrecognized command-line option '-mauto-litpools'

reveals that the target's CFLAGS are being used for host compilation.
The patch fixes the host compilation by correctly setting the CFLAGS to
be used.

It should be noted that the build script used by ntpsec applies CFLAGS
for host compilation and --cross-cflags for target compilation.

Fixes:
 - http://autobuild.buildroot.org/results/9321a637f2c340ce8dcb24249676bb6c44d0dfc6

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 064e4c09fa788ccf0927fcaf3987e0f0fdc08eb7)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ntpsec/ntpsec.mk

@@ -42,6 +42,7 @@ NTPSEC_DEPENDENCIES = \
 # --cross-compiler
 NTPSEC_CONF_OPTS = \
 	CC="$(HOSTCC)" \
+	CFLAGS="$(HOST_CFLAGS)" \
 	PYTHON_CONFIG="$(STAGING_DIR)/usr/bin/python3-config" \
 	--libdir=/usr/lib/python$(PYTHON3_VERSION_MAJOR)/site-packages/ntp \
 	--cross-compiler="$(TARGET_CC)" \