treewide: fix #include errors after gcc-5.4

They were mostly missing <cmath> or <math.h>.

pkgs/applications/graphics/leocad/default.nix

@@ -17,6 +17,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ qt4 qmake4Hook zlib ];
 
   postPatch = ''
+    sed '1i#include <cmath>' -i common/camera.cpp
     substituteInPlace common/camera.cpp --replace "isnan(" "std::isnan("
     export qmakeFlags="$qmakeFlags INSTALL_PREFIX=$out"
   '';