treewide: fix #include errors after gcc-5.4

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

pkgs/misc/emulators/higan/default.nix

@@ -21,6 +21,7 @@ stdenv.mkDerivation rec {
   };
 
   patches = [ ./0001-change-flags.diff ];
+  postPatch = "sed '1i#include <cmath>' -i higan/fc/ppu/ppu.cpp";
 
   buildInputs =
   [ p7zip pkgconfig libX11 libXv udev mesa SDL libao openal libpulseaudio gtk gtksourceview ];

pkgs/misc/emulators/pcsx2/default.nix

@@ -15,6 +15,8 @@ stdenv.mkDerivation rec {
     sha256 = "0s7mxq2cgzwjfsq0vhpz6ljk7wr725nxg48128iyirf85585l691";
   };
 
+  postPatch = "sed '1i#include \"x86intrin.h\"' -i common/src/x86emitter/cpudetect.cpp";
+
   configurePhase = ''
     mkdir -p build
     cd build
@@ -50,6 +52,8 @@ stdenv.mkDerivation rec {
     soundtouch wxGTK30 zlib
   ];
 
+  enableParallelBuilding = true;
+
   meta = with stdenv.lib; {
     description = "Playstation 2 emulator";
     longDescription= ''