update build system

scripts/env.sh

@@ -230,6 +230,12 @@ fi
 
 PATH="${PROJECT_EXTERNAL_BUILD_ROOT}/bin:${PATH}"
 
+if [ "${PROJECT_IS_MINGW}" == "1" ]; then
+  PROJECT_OS=win32
+else
+  PROJECT_OS=linux
+fi
+
 export MSYS
 export NUM_JOBS
 export OPENSSL_ROOT_DIR
@@ -254,6 +260,7 @@ export PROJECT_LINK_TYPE
 export PROJECT_MINGW64_COPY_DEPENDENCIES
 export PROJECT_MINGW64_DOCKER_BUILD_ARGS
 export PROJECT_MSYS2_PACKAGE_LIST
+export PROJECT_OS
 export PROJECT_PRIVATE_KEY
 export PROJECT_PUBLIC_KEY
 export PROJECT_REQUIRE_ALPINE