ebtks: fix build on darwin

pkgs/by-name/eb/ebtks/package.nix

@@ -15,6 +15,10 @@ stdenv.mkDerivation {
   postPatch = ''
     substituteInPlace templates/EBTKS/SimpleArray.h \
       --replace "#define FINITE(x) finite(x)" "#define FINITE(x) isfinite(x)"
+  ''
+  # error: ISO C++17 does not allow 'register' storage class specifier
+  + ''
+    find . -type f -exec sed -i -e 's/register //g' {} +
   '';
 
   nativeBuildInputs = [ cmake ];