package/minisign: do not strip

Set CMAKE_STRIP to an empty value to avoid the following build failure
with BR2_BINFMT_FLAT raised since the addition of the package in commit
d90ac63d9b3448a239bb9aa8030326699a3fdc3d:

/home/buildroot/instance-0/output-1/host/bin/m68k-linux-strip: /home/buildroot/instance-0/output-1/build/minisign-0.11/minisign: file format not recognized

Fixes: d90ac63d9b3448a239bb9aa8030326699a3fdc3d
 - http://autobuild.buildroot.org/results/9cc9fd17c7eb4a741c08f27f69764df4a26295fa

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/minisign/minisign.mk

@@ -10,6 +10,7 @@ MINISIGN_LICENSE = ISC
 MINISIGN_LICENSE_FILES = LICENSE
 MINISIGN_DEPENDENCIES = libsodium
 HOST_MINISIGN_DEPENDENCIES = host-libsodium
+MINISIGN_CONF_OPTS = -DCMAKE_STRIP=""
 
 ifeq ($(BR2_STATIC_LIBS),y)
 MINISIGN_CONF_OPTS += -DBUILD_STATIC_EXECUTABLES=1