aws-sdk-cpp: fix cross-OS crosscompilation (#133182)

The TARGET_ARCH cmake variable is used to specify the host OS, which if
unspecified defaults to the same as the build OS. So to crosscompile
aws-sdk-cpp to another OS, the TARGET_ARCH variable must be specified.

Example hydra failure: https://hydra.nixos.org/build/149290553/nixlog/3

pkgs/development/libraries/aws-sdk-cpp/default.nix

···
   customMemoryManagement ? true
 }:
 
+let
+  host_os = if stdenv.hostPlatform.isDarwin then "APPLE"
+       else if stdenv.hostPlatform.isAndroid then "ANDROID"
+       else if stdenv.hostPlatform.isWindows then "WINDOWS"
+       else if stdenv.hostPlatform.isLinux then "LINUX"
+       else throw "Unknown host OS";
+in
+
 stdenv.mkDerivation rec {
   pname = "aws-sdk-cpp";
   version = "1.8.130";
···
     "-DENABLE_TESTING=OFF"
     "-DCURL_HAS_H2=1"
     "-DCURL_HAS_TLS_PROXY=1"
+    "-DTARGET_ARCH=${host_os}"
   ] ++ lib.optional (apis != ["*"])
     "-DBUILD_ONLY=${lib.concatStringsSep ";" apis}";