add cmake helper vars

scripts/toolchain.cmake.in

@@ -0,0 +1,10 @@
+set(CMAKE_SYSTEM_NAME Linux)
+set(CMAKE_C_COMPILER @@TARGET_CC@@)
+set(CMAKE_CXX_COMPILER @@TARGET_CXX@@)
+set(CMAKE_INSTALL_SO_NO_EXE 0)
+set(CMAKE_PROGRAM_PATH \"@@STAGING_HOST_DIR@@/usr/bin\")
+set(CMAKE_FIND_ROOT_PATH \"@@STAGING_TARGET_DIR@@\")
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(ENV{PKG_CONFIG_SYSROOT_DIR} \"@@STAGING_TARGET_DIR@@\")