python-selenium: fix darwin build

/cc ZHF #36454

pkgs/development/python-modules/selenium/default.nix

@@ -7,6 +7,19 @@
 , xorg
 }:
 
+
+let
+  # Recompiling x_ignore_nofocus.so as the original one dlopen's libX11.so.6 by some
+  # absolute paths. Replaced by relative path so it is found when used in nix.
+  x_ignore_nofocus =
+    fetchFromGitHub {
+      owner = "SeleniumHQ";
+      repo = "selenium";
+      rev = "selenium-3.6.0";
+      sha256 = "13wf4hx4i7nhl4s8xkziwxl0km1j873syrj4amragj6mpip2wn8v";
+    };
+in
+
 buildPythonPackage rec {
   pname = "selenium";
   version = "3.6.0";
@@ -23,21 +36,11 @@ buildPythonPackage rec {
     geckodriver
   ];
 
-  # Recompiling x_ignore_nofocus.so as the original one dlopen's libX11.so.6 by some
+  patchPhase = stdenv.lib.optionalString stdenv.isLinux ''
-  # absolute paths. Replaced by relative path so it is found when used in nix.
-  x_ignore_nofocus =
-    fetchFromGitHub {
-      owner = "SeleniumHQ";
-      repo = "selenium";
-      rev = "selenium-3.6.0";
-      sha256 = "13wf4hx4i7nhl4s8xkziwxl0km1j873syrj4amragj6mpip2wn8v";
-    };
-
-  patchPhase = ''
     cp "${x_ignore_nofocus}/cpp/linux-specific/"* .
     substituteInPlace x_ignore_nofocus.c --replace "/usr/lib/libX11.so.6" "${xorg.libX11.out}/lib/libX11.so.6"
-    gcc -c -fPIC x_ignore_nofocus.c -o x_ignore_nofocus.o
+    cc -c -fPIC x_ignore_nofocus.c -o x_ignore_nofocus.o
-    gcc -shared \
+    cc -shared \
       -Wl,${if stdenv.isDarwin then "-install_name" else "-soname"},x_ignore_nofocus.so \
       -o x_ignore_nofocus.so \
       x_ignore_nofocus.o