swupdate: Disable partition algorith when LTO is enabled

-flto-partition=none is needed when building with -flto
Use += to add libconfig to depends, so it does not overwrite the
programmatically added dependencies
Signed-off-by: Khem Raj <raj.khem@gmail.com>

recipes-support/swupdate/swupdate.inc

 SUMMARY="Image updater for Yocto projects"
 DESCRIPTION = "Application for automatic software update from USB Pen"
 SECTION="swupdate"
-DEPENDS = "libconfig"
+DEPENDS += "libconfig"
 
 # SWUpdate licensing is described in the following pages:
 # https://sbabic.github.io/swupdate/licensing.html
@@ -30,6 +30,8 @@ SRC_URI = "git://github.com/sbabic/swupdate.git;protocol=https \
     file://90-start-progress \
 "
 
+LTOEXTRA += "-flto-partition=none"
+
 PACKAGES =+ " \
     ${PN}-client \
     ${PN}-lua \