CI: Add scan-build

Run scan-build (clang-tools based) static analyzer on all build
variants.

.travis.yml

@@ -1,14 +1,23 @@
 language: cpp
+
+addons:
+  apt:
+    packages:
+      # Need for scan-build
+      - clang-tools
 matrix:
   include:
   - os: linux
+    dist: bionic
     compiler: gcc
   - os: linux
+    dist: bionic
     compiler: clang
   - os: osx
+
 script:
-- make -C tests EXTRA_CFLAGS="-W -Wall -Wextra"
-- make -C tests clean ; make -C tests pedantic
-- make -C tests clean ; make -C tests pedantic EXTRA_CFLAGS=-DNO_DECLTYPE
-- make -C tests clean ; make -C tests cplusplus
-- make -C tests clean ; make -C tests cplusplus EXTRA_CFLAGS=-DNO_DECLTYPE
+- scan-build make -C tests EXTRA_CFLAGS="-W -Wall -Wextra"
+- make -C tests clean ; scan-build make -C tests pedantic
+- make -C tests clean ; scan-build make -C tests pedantic EXTRA_CFLAGS=-DNO_DECLTYPE
+- make -C tests clean ; scan-build make -C tests cplusplus
+- make -C tests clean ; scan-build make -C tests cplusplus EXTRA_CFLAGS=-DNO_DECLTYPE