Makefile: no darwin+arm windows+arm build matrix

This commit excludes Darwin+ARM and Windows+ARM combinations from the
build matrix.

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

.travis.yml

@@ -21,6 +21,8 @@ install: true
 script:
   - make
   - make all-build
+  - make OS=darwin
+  - make OS=windows
   - make clean
   - make unit
   - make lint

Makefile

@@ -59,7 +59,7 @@ push-latest-%:
 push-%:
 	@$(MAKE) --no-print-directory ARCH=$* push
 
-all-build: $(foreach os, $(ALL_OS), $(addprefix build-$(os)-, $(ALL_ARCH)))
+all-build: $(addprefix build-$(OS)-, $(ALL_ARCH))
 
 all-container: $(addprefix container-, $(ALL_ARCH))