treewide: fix #include errors after gcc-5.4

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

pkgs/development/libraries/botan/generic.nix

@@ -2,6 +2,7 @@
 # Passed by version specific builders
 , baseVersion, revision, sha256
 , extraConfigureFlags ? ""
+, postPatch ? null
 , ...
 }:
 
@@ -17,6 +18,7 @@ stdenv.mkDerivation rec {
     ];
     inherit sha256;
   };
+  inherit postPatch;
 
   buildInputs = [ python bzip2 zlib gmp openssl boost ];