package/socat: fix printf feature detection

socal configure uses AC_TRY_RUN to detect printf features. This does
not work for cross compilation.

All C libraries we use support C99 snprintf. Only glibc and uClibc
support the deprecated Z modifier.

These issues were noticed by an inspection of configure.ac.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/socat/socat.mk

@@ -11,6 +11,14 @@ SOCAT_LICENSE = GPL-2.0 with OpenSSL exception
 SOCAT_LICENSE_FILES = README COPYING COPYING.OpenSSL
 SOCAT_CPE_ID_VENDOR = dest-unreach
 
+SOCAT_CONF_ENV = ac_cv_have_c99_snprintf=yes
+
+ifeq ($(BR2_TOOLCHAIN_USES_GLIBC)$(BR2_TOOLCHAIN_USES_UCLIBC),y)
+SOCAT_CONF_ENV += ac_cv_have_z_modifier=yes
+else
+SOCAT_CONF_ENV += ac_cv_have_z_modifier=no
+endif
+
 ifeq ($(BR2_powerpc)$(BR2_powerpc64)$(BR2_powerpc64le),y)
 SOCAT_CONF_ENV += \
 	sc_cv_sys_crdly_shift=12 \