build: do not warn about ARM ABI differences between GCC versions

This is Buildroot, we're rebuilding all the time, so there's no value in
adding a "note" from the compiler (it's not a warning, it's a note)
about some ABI-incompatible changes. If we're upgrading the toolchain,
we are rebuilding at the same time for sure, this is Buildroot after
all.

Change-Id: Ie5018681ebe7478abe792c35931f104b90a40575
diff --git a/configs/czechlight_beaglebone_defconfig b/configs/czechlight_beaglebone_defconfig
index 563e628..d43a1ab 100644
--- a/configs/czechlight_beaglebone_defconfig
+++ b/configs/czechlight_beaglebone_defconfig
@@ -9,6 +9,7 @@
 BR2_SSP_STRONG=y
 BR2_TOOLCHAIN_EXTERNAL=y
 BR2_TOOLCHAIN_EXTERNAL_GDB_SERVER_COPY=y
+BR2_TARGET_OPTIMIZATION="-Wno-psabi"
 BR2_TARGET_GENERIC_HOSTNAME="czechlight"
 BR2_TARGET_GENERIC_ISSUE="Welcome to Czech Light"
 BR2_INIT_SYSTEMD=y