Makefile: keep cmake-build as default target (#2579)

Fixes https://github.com/awesomeWM/awesome/issues/2576.

.travis.yml

@@ -247,9 +247,6 @@ script:
         git checkout "$commit"
         git --no-pager show --stat
 
-        # Remove/clean any existing build dir.
-        sudo make distclean
-
         if ! make all check CMAKE_ARGS+="-D DO_COVERAGE=0"; then
           failed="$failed $commit"
         fi

Makefile

@@ -7,7 +7,12 @@ endif
 
 BUILDDIR=build
 
-all: awesome ;
+# Run "make" in $(BUILDDIR) by default.
+# This is required to generate all files already, which should not be generated
+# with "(sudo) make install" only later.
+cmake-build: $(BUILDDIR)/Makefile
+	$(ECHO) "Building…"
+	$(MAKE) -C $(BUILDDIR)
 
 $(BUILDDIR)/Makefile:
 	$(ECHO) "Creating build directory and running cmake in it. You can also run CMake directly, if you want."