Remove hard-coded __AVR__ in favor of platform configuration

Author: ianfixes

CHANGELOG.md

@@ -7,7 +7,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 ### Added
-- Add `__AVR__` to defines when compiling
 - `arduino_ci_remote.rb` CLI switch `--skip-examples-compilation`
 - Add support for `diditalPinToPort()`, `digitalPinToBitMask()`, and `portOutputRegister()`
 - `CppLibrary.header_files` to find header files

lib/arduino_ci/cpp_library.rb

@@ -398,7 +398,7 @@ def build_for_test_with_configuration(test_file, aux_libraries, gcc_binary, ci_g
       executable = Pathname.new("unittest_#{base}.bin").expand_path
       File.delete(executable) if File.exist?(executable)
       arg_sets = []
-      arg_sets << ["-std=c++0x", "-o", executable.to_s, "-DARDUINO=100", "-D__AVR__"]
+      arg_sets << ["-std=c++0x", "-o", executable.to_s, "-DARDUINO=100"]
       if libasan?(gcc_binary)
         arg_sets << [ # Stuff to help with dynamic memory mishandling
           "-g", "-O1",