Merge 'mingw-w64' and 'darwin' into cross-win-osx.

Both branches have quite a lot in common, so it's time for a merge and
do the cleanups with respect to both implementations and also generalize
both implementations as much as possible.

This also closes #1876.

Conflicts:
	pkgs/development/interpreters/lua-5/5.2.nix
	pkgs/development/libraries/SDL/default.nix
	pkgs/development/libraries/glew/default.nix
	pkgs/top-level/all-packages.nix

pkgs/development/libraries/openssl/cert-file.patch

@@ -12,7 +12,7 @@ diff -ru -x '*~' openssl-1.0.0e-orig/crypto/x509/x509_def.c openssl-1.0.0e/crypt
  #include "cryptlib.h"
  #include <openssl/crypto.h>
  #include <openssl/x509.h>
-@@ -71,7 +75,19 @@
+@@ -71,7 +75,25 @@
  	{ return(X509_CERT_DIR); }
  
  const char *X509_get_default_cert_file(void)
@@ -23,9 +23,15 @@ diff -ru -x '*~' openssl-1.0.0e-orig/crypto/x509/x509_def.c openssl-1.0.0e/crypt
 +	if (!init) {
 +	    init = 1;
 +	    char * s = getenv("OPENSSL_X509_CERT_FILE");
-+	    if (s && getuid() == geteuid()) {
-+		strncpy(buf, s, sizeof(buf));
-+		buf[sizeof(buf) - 1] = 0;
++	    if (s) {
++#ifndef OPENSSL_SYS_WINDOWS
++	        if (getuid() == geteuid()) {
++#endif
++		        strncpy(buf, s, sizeof(buf));
++		        buf[sizeof(buf) - 1] = 0;
++#ifndef OPENSSL_SYS_WINDOWS
++	        }
++#endif
 +	    }
 +	}
 +	return buf;

pkgs/development/libraries/openssl/default.nix

@@ -8,7 +8,9 @@ let
     (throw "openssl needs its platform name cross building" null)
     stdenv.cross;
 
-  patchesCross = isCross:
+  patchesCross = isCross: let
+    isDarwin = stdenv.isDarwin || (isCross && stdenv.cross.libc == "libSystem");
+  in
     [ # Allow the location of the X509 certificate file (the CA
       # bundle) to be set through the environment variable
       # ‘OPENSSL_X509_CERT_FILE’.  This is necessary because the
@@ -29,7 +31,7 @@ let
           ./kfreebsd-gnu.patch
         ]
 
-    ++ stdenv.lib.optional stdenv.isDarwin ./darwin-arch.patch;
+    ++ stdenv.lib.optional isDarwin ./darwin-arch.patch;
 
 in
 
@@ -91,6 +93,8 @@ stdenv.mkDerivation {
       rm $out/bin/c_rehash $out/ssl/misc/CA.pl $out/ssl/misc/tsget
     '';
     configureScript = "./Configure";
+  } // stdenv.lib.optionalAttrs (opensslCrossSystem == "darwin64-x86_64-cc") {
+    CC = "gcc";
   };
 
   meta = {