Improve the header includes, cont'd

Also check in the modulemap file, and add a option to build with clang's
-fmodules.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/compton.modulemap

@@ -0,0 +1,84 @@
+// modulemap
+// Generated by: modularize -module-map-path=modulemap list -I. -I/usr/include/pixman-1 -x c -I/usr/include/dbus-1.0 -DCONFIG_XINERAMA -DCONFIG_LIBCONFIG -DCONFIG_REGEX_PCRE -DCONFIG_REGEX_PCRE_JIT -DCONFIG_OPENGL -DCONFIG_DBUS -DGL_GLEXT_PROTOTYPES -I/usr/lib/dbus-1.0/include
+
+module compiler {
+  header "compiler.h"
+}
+module string_utils {
+  header "string_utils.h"
+}
+module dbus {
+  header "dbus.h"
+}
+module kernel {
+  header "kernel.h"
+}
+module utils {
+  header "utils.h"
+}
+module region {
+  header "region.h"
+}
+module compton {
+  header "compton.h"
+  exclude header "/usr/include/X11/Xlib.h"
+}
+module types {
+  header "types.h"
+}
+module c2 {
+  header "c2.h"
+}
+module render {
+  header "render.h"
+}
+module options {
+  header "options.h"
+}
+module opengl {
+  header "opengl.h"
+}
+module diagnostic {
+  header "diagnostic.h"
+}
+module win {
+  header "win.h"
+  exclude header "/usr/include/GL/glx.h"
+}
+module log {
+  header "log.h"
+}
+module x {
+  header "x.h"
+}
+module vsync {
+  header "vsync.h"
+}
+module common {
+  header "common.h"
+  exclude header "/usr/include/X11/Xlib.h"
+  exclude header "/usr/include/GL/glx.h"
+}
+module config {
+  header "config.h"
+}
+module xrescheck {
+  header "xrescheck.h"
+}
+module backend {
+  module gl {
+    module gl_common {
+      header "backend/gl/gl_common.h"
+    }
+  }
+  module backend {
+    header "backend/backend.h"
+  }
+  module backend_common {
+    header "backend/backend_common.h"
+  }
+}
+module Xlib {
+  header "/usr/include/X11/Xlib.h"
+  export *
+}