Fix 32-bit build issues on Travis-CI by installing multilib

If, longer term, the Travis-CI support for 32-bit is inconsistent
the lines that failed are:
 - make -s DEBUG=-m32
 - cd ../example_3 && rake
Add target 'ci' for building examples with -Werror

.travis.yml

@@ -11,6 +11,7 @@ matrix:
 
 before_install:
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then rvm install 2.1 && rvm use 2.1 && ruby -v; fi
+  - if [ "$TRAVIS_OS_NAME" == "linux" ]; then sudo apt-get install --assume-yes --quiet gcc-multilib; fi
 install: gem install rspec
 script:
   - cd test && rake ci
@@ -19,6 +20,6 @@ script:
   - cd ../extras/fixture/test && rake ci
   - make -s default noStdlibMalloc
   - make -s C89
-  - cd ../../../examples/example_1 && make -s
-  - cd ../example_2 && make -s
+  - cd ../../../examples/example_1 && make -s ci
+  - cd ../example_2 && make -s ci
   - cd ../example_3 && rake

examples/example_1/makefile

@@ -67,3 +67,5 @@ test/test_runners/TestProductionCode2_Runner.c: test/TestProductionCode2.c
 clean:
 	$(CLEANUP) $(TARGET1) $(TARGET2)
 
+ci: CFLAGS += -Werror
+ci: default

examples/example_2/makefile

@@ -66,3 +66,5 @@ default:
 clean:
 	$(CLEANUP) $(TARGET1)
 
+ci: CFLAGS += -Werror
+ci: default