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/build-support/gcc-cross-wrapper/builder.sh

@@ -26,6 +26,10 @@ if test -z "$nativeLibc"; then
       fi
     fi
 
+    if [ -n "$osxMinVersion" ]; then
+        cflagsCompile="$cflagsCompile -mmacosx-version-min=$osxMinVersion"
+    fi
+
     echo "$cflagsCompile -B$libc/lib/ -idirafter $libc/include -idirafter $gcc/lib/gcc/*/*/include-fixed" > $out/nix-support/libc-cflags
 
     echo "-L$libc/lib -rpath $libc/lib -rpath-link $libc/lib" > $out/nix-support/libc-ldflags

pkgs/build-support/gcc-cross-wrapper/default.nix

@@ -46,6 +46,7 @@ stdenv.mkDerivation {
   addFlags = ./add-flags;
   inherit nativeTools nativeLibc nativePrefix gcc libc binutils;
   crossConfig = if cross != null then cross.config else null;
+  osxMinVersion = cross.osxMinVersion or null;
   gccLibs = if gcc != null then gccLibs else null;
   name = chosenName;
   langC = if nativeTools then true else gcc.langC;

pkgs/build-support/gcc-cross-wrapper/setup-hook.sh

@@ -70,11 +70,16 @@ fi
 
 if test "$dontSetConfigureCross" != "1"; then
     configureFlags="$configureFlags --build=$system --host=$crossConfig"
+    # This is because -print-prog-name tries to search FHS paths.
+    configureFlags="$configureFlags LD=$crossConfig-ld"
 fi
 # Disabling the tests when cross compiling, as usually the tests are meant for
 # native compilations.
 doCheck=""
 
+# Don't strip foreign binaries with native "strip" tool.
+dontStrip=1
+
 # Add the output as an rpath.
 if test "$NIX_NO_SELF_RPATH" != "1"; then
     export NIX_CROSS_LDFLAGS="-rpath $out/lib -rpath-link $out/lib $NIX_CROSS_LDFLAGS"