add various missing headers

Fixes building with gcc-4.8

Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>

src/ConfigGlobal.cxx

@@ -32,6 +32,7 @@
 
 #include <assert.h>
 #include <string.h>
+#include <stdlib.h>
 
 static ConfigData config_data;
 

src/InotifySource.cxx

@@ -27,6 +27,7 @@
 
 #include <sys/inotify.h>
 #include <unistd.h>
+#include <errno.h>
 
 bool
 InotifySource::OnSocketReady(gcc_unused unsigned flags)

src/system/FatalError.cxx

@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <stdarg.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 #ifdef WIN32
 #include <windows.h>