Fix problem with warnings (Arduino-CI#297).

Author: James Foster

SampleProjects/TestSomething/.arduino-ci.yml

@@ -1,3 +1,18 @@
+platforms:
+   uno:
+     board: arduino:avr:uno
+     package: arduino:avr
+     gcc:
+       features:
+       defines:
+         - __AVR__
+         - __AVR_ATmega328P__
+         - ARDUINO_ARCH_AVR
+         - ARDUINO_AVR_UNO
+       warnings:
+         - no-unknown-attributes
+       flags:
+
 unittest:
   platforms:
     - uno

lib/arduino_ci/cpp_library.rb

@@ -443,7 +443,7 @@ def feature_args(ci_gcc_config)
     def warning_args(ci_gcc_config)
       return [] if ci_gcc_config[:warnings].nil?
 
-      ci_gcc_config[:features].map { |w| "-W#{w}" }
+      ci_gcc_config[:warnings].map { |w| "-W#{w}" }
     end
 
     # GCC command line arguments for defines (e.g. -Dhave_something)