package/ntp: override host shell check

Add a patch from the upstream AutoGen package that allows POSIX_SHELL
to be taken from the environment, then define that to be '/bin/sh'.

Since we are cross-compiling, the original behaviour of detecting the
host shell is not useful as we cannot assume that the target uses the
same shell, and it can prevent builds being reproducible because a
different host environment will result in a different target binary.

Signed-off-by: James Byrne <james.byrne@origamienergy.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/ntp/0003-override-shell.patch

@@ -0,0 +1,20 @@
+sntp/libopts/m4/libopts.m4: allow override shell with POSIX_SHELL
+
+Pull in fix from upstream AutoGen [1] to accept POSIX_SHELL from the
+environment during the configure step.
+
+[1] http://git.savannah.gnu.org/cgit/autogen.git/commit/?id=db064b9a252f3ef3d8db25411ea0edb0ff8ea758
+
+Signed-off-by: James Byrne <james.byrne@origamienergy.com>
+
+diff --git a/sntp/libopts/m4/libopts.m4 b/sntp/libopts/m4/libopts.m4
+--- a/sntp/libopts/m4/libopts.m4
++++ b/sntp/libopts/m4/libopts.m4
+@@ -114,6 +114,7 @@
+   AC_PROG_SED
+   [while :
+   do
++      test -x "$POSIX_SHELL" && break
+       POSIX_SHELL=`which bash`
+       test -x "$POSIX_SHELL" && break
+       POSIX_SHELL=`which dash`

package/ntp/ntp.mk

@@ -10,7 +10,7 @@ NTP_SITE = https://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-$(NTP_VERSION_MAJO
 NTP_DEPENDENCIES = host-pkgconf libevent
 NTP_LICENSE = NTP
 NTP_LICENSE_FILES = COPYRIGHT
-NTP_CONF_ENV = ac_cv_lib_md5_MD5Init=no
+NTP_CONF_ENV = ac_cv_lib_md5_MD5Init=no POSIX_SHELL=/bin/sh
 NTP_CONF_OPTS = \
 	--with-shared \
 	--program-transform-name=s,,, \