Use static library for automatic compiler detection

There has been a long standing bug with cmake that does not
allow it to properly detect embedded compilers (we have to
call "generate_makefile" twice because of this bug).

With CMake 3.6 we can finally tell CMake to use static libs
for the detection to circumvent the problem!

toolchains/arm-none-eabi.cmake

@@ -1,3 +1,5 @@
+SET(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
 # the name of the target operating system
 SET(CMAKE_SYSTEM_NAME Generic)