Fix build on FreeBSD

- Make sure CMake always finds absolute paths for Cairo, Pango and GdkPixbuf
- Add forgotten json-c include path to swaymsg/CMakeLists.txt
- Disable -Werror because of assert warnings
- Add correct /proc/pid/file path for FreeBSD
- Use libepoll-shim on FreeBSD
- Only use Linux capabilities on, well, Linux

sway/CMakeLists.txt

@@ -55,9 +55,12 @@ target_link_libraries(sway
 	${PANGO_LIBRARIES}
 	${JSONC_LIBRARIES}
 	m
-    cap
 )
 
+if (CMAKE_SYSTEM_NAME STREQUAL Linux)
+	target_link_libraries(sway cap)
+endif (CMAKE_SYSTEM_NAME STREQUAL Linux)
+
 install(
 	TARGETS sway
 	RUNTIME

sway/ipc-server.c

@@ -126,6 +126,8 @@ struct sockaddr_un *ipc_user_sockaddr(void) {
 }
 
 static pid_t get_client_pid(int client_fd) {
+// FreeBSD supports getting uid/gid, but not pid
+#ifdef __linux__
 	struct ucred ucred;
 	socklen_t len = sizeof(struct ucred);
 
@@ -134,6 +136,9 @@ static pid_t get_client_pid(int client_fd) {
 	}
 
 	return ucred.pid;
+#else
+	return -1;
+#endif
 }
 
 int ipc_handle_connection(int fd, uint32_t mask, void *data) {

sway/main.c

@@ -152,6 +152,7 @@ static void security_sanity_check() {
 		sway_log(L_ERROR,
 			"!! DANGER !! /proc is not available - sway CANNOT enforce security rules!");
 	}
+#ifdef __linux__
 	cap_flag_value_t v;
 	cap_t cap = cap_get_proc();
 	if (!cap || cap_get_flag(cap, CAP_SYS_PTRACE, CAP_PERMITTED, &v) != 0 || v != CAP_SET) {
@@ -161,6 +162,7 @@ static void security_sanity_check() {
 	if (cap) {
 		cap_free(cap);
 	}
+#endif
 	if (!stat(SYSCONFDIR "/sway", &s)) {
 		if (s.st_uid != 0 || s.st_gid != 0
 				|| (s.st_mode & S_IWGRP) || (s.st_mode & S_IWOTH)) {

sway/security.c

@@ -28,7 +28,11 @@ struct command_policy *alloc_command_policy(const char *command) {
 }
 
 enum secure_feature get_feature_policy(pid_t pid) {
+#ifdef __FreeBSD__
+	const char *fmt = "/proc/%d/file";
+#else
 	const char *fmt = "/proc/%d/exe";
+#endif
 	int pathlen = snprintf(NULL, 0, fmt, pid);
 	char *path = malloc(pathlen + 1);
 	snprintf(path, pathlen + 1, fmt, pid);