Build with gcc 4.7
https://bugs.gentoo.org/show_bug.cgi?id=421913

Index: hydrogen-0.9.5/gui/src/MainForm.cpp
===================================================================
--- hydrogen-0.9.5.orig/gui/src/MainForm.cpp
+++ hydrogen-0.9.5/gui/src/MainForm.cpp
@@ -70,6 +70,7 @@ using namespace H2Core;
 
 #include <memory>
 #include <cassert>
+#include <unistd.h>
 
 using namespace std;
 using namespace H2Core;
Index: hydrogen-0.9.5/gui/src/SongEditor/SongEditor.cpp
===================================================================
--- hydrogen-0.9.5.orig/gui/src/SongEditor/SongEditor.cpp
+++ hydrogen-0.9.5/gui/src/SongEditor/SongEditor.cpp
@@ -21,6 +21,7 @@
  */
 
 #include <assert.h>
+#include <unistd.h>
 #include <algorithm>
 #include <memory>