Increment @failure_count if build_shared_library fails

Author: hlovdal

Diff for: CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fix missing `LED_BUILTIN` definition for Arduino Due, Zero and Circuit Playground.
+- No longer ignore failures if the first step of compiling files for the
+  unit test fails.
 
 ### Security
 

Diff for: exe/arduino_ci.rb

@@ -436,7 +436,9 @@ def perform_unit_tests(cpp_library, file_config)
     puts
     compilers.each do |gcc_binary|
       # before compiling the tests, build a shared library of everything except the test code
-      next unless build_shared_library(gcc_binary, p, config, cpp_library)
+      build_result = build_shared_library(gcc_binary, p, config, cpp_library)
+      @failure_count += 1 unless build_result
+      next unless build_result
 
       # now build and run each test using the shared library build above
       config.allowable_unittest_files(cpp_library.test_files).each do |unittest_path|