build: Add alpine to CI for tests with musl libc

Closes: !18
Signed-off-by: Guillem Jover <guillem@hadrons.org>

.gitlab-ci.yml

@@ -1,19 +1,37 @@
-image: debian:buster
+.unit-tests:
+  script:
+    - ./autogen && ./configure
+    - make check
 
+.coverage:
+  script:
+    - ./autogen && ./configure --disable-static
+    - make check CFLAGS="--coverage -O0 -ggdb" LDFLAGS="--coverage -O0 -ggdb"
+    - gcovr -s -e test/
+
+.debian:
+  image: debian:buster
+  stage: test
   before_script:
     - apt-get update -qq
     - apt-get install -qq -y --no-install-recommends
               git gcc make autoconf automake libtool libmd-dev gcovr
 
-unit-tests:
+.alpine:
+  image: alpine:latest
   stage: test
-  script:
-    - ./autogen && ./configure
-    - make check
+  before_script:
+    - apk add --no-cache git gcc make autoconf automake libtool
+              bsd-compat-headers linux-headers libmd-dev musl-dev gcovr
 
-coverage:
-  stage: test
-  script:
-    - ./autogen && ./configure --disable-static
-    - make check CFLAGS="--coverage -O0 -ggdb" LDFLAGS="--coverage -O0 -ggdb"
-    - gcovr -s -e test/
+unit-tests:debian:
+  extends: [.debian, .unit-tests]
+
+coverage:debian:
+  extends: [.debian, .coverage]
+
+unit-tests:alpine:
+  extends: [.alpine, .unit-tests]
+
+coverage:alpine:
+  extends: [.alpine, .coverage]