Add libcap check to CMake

- Moved ``<sys/capability.h>`` include inside `__linux__` guard,
  because all uses are similarly guarded.
- <sys/capability.h> is part of an optional devel package, at least
  in fedora. CMake now explicitly checks that libcap devel files
  are available.
- Added libcap to the list of install packages in .travis.yml, to
  make the dependency explicit. travis-ci installs the package by
  default, which is why this hasn't surfaced previously.

1 files changed, 1 insertions, 1 deletions

diff --git a/sway/main.c b/sway/main.c
index 55b71fa4..b9f8936f 100644
--- a/sway/main.c
+++ b/sway/main.c
@@ -11,8 +11,8 @@
 #include <signal.h>
 #include <unistd.h>
 #include <getopt.h>
-#include <sys/capability.h>
 #ifdef __linux__
+#include <sys/capability.h>
 #include <sys/prctl.h>
 #endif
 #include "sway/extensions.h"