Silence irrelevant compiler notes about GCC ABI incompatibilities

There are ABI changes between GCC 6.x and 7.1 that make them
incompatible, but that is not relevant here since all software is
compiled with only one GCC version.

Change-Id: If82f874162404bdedc9c2e93c3a8c7a6d648fde0
diff --git a/cmake/toolchain/arm-none-eabi-gcc.cmake b/cmake/toolchain/arm-none-eabi-gcc.cmake
index ec10b2f..ce54cd5 100644
--- a/cmake/toolchain/arm-none-eabi-gcc.cmake
+++ b/cmake/toolchain/arm-none-eabi-gcc.cmake
@@ -105,4 +105,6 @@
     -Wunused
 
     -Wno-redundant-decls
+
+    -Wno-psabi
 )