Explicitly include headers for PCH free build (#312)

There are some headers that implicitly included by PCH. Include those
explicitly so PCH free build succeeds.

src/components/channellist/classic/guildlist.cpp

@@ -1,3 +1,5 @@
+#include <gtkmm/overlay.h>
+
 #include "guildlist.hpp"
 
 #include "abaddon.hpp"

src/components/channellist/classic/mentionoverlay.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <set>
+
 #include <gtkmm/drawingarea.h>
 #include <pangomm/fontdescription.h>
 

src/misc/cairo.cpp

@@ -1,7 +1,5 @@
 #include "cairo.hpp"
 
-#include <cairomm/context.h>
-
 constexpr static double M_PI_H = M_PI / 2.0;
 constexpr static double M_PI_3_2 = M_PI * 3.0 / 2.0;
 

src/misc/cairo.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <cairomm/context.h>
+
 namespace CairoUtil {
 void PathRoundedRect(const Cairo::RefPtr<Cairo::Context> &cr, double x, double y, double w, double h, double r);
 } // namespace CairoUtil

src/platform.cpp

@@ -7,6 +7,9 @@
 #ifdef __APPLE__
     #include <unistd.h>
 #endif
+#ifdef __linux__
+    #include "util.hpp"
+#endif
 
 #include <spdlog/spdlog.h>