Support Clang/LLVM build on FBSD

- Update CMakeList to support installation to PREFIX directory
- FreeBSD does not support abstract sockets (unix-abstract:laminar),
  so explicit 'LAMINAR_BIND_RPC=IP:port' is required
- ld.lld requires explicit emulation for binary blobs, add a new
  variable LINKER_EMULATION_FLAGS for this purpose

src/server.cpp

@@ -28,9 +28,8 @@
 
 #include <signal.h>
 #include <sys/eventfd.h>
-#include <sys/inotify.h>
-#include <sys/signalfd.h>
 #include <sys/stat.h>
+#include <sys/inotify.h>
 
 // Size of buffer used to read from file descriptors. Should be
 // a multiple of sizeof(struct signalfd_siginfo) == 128