toolchain: Do not pollute TOOLCHAIN_HOME

Use it's own variable HOST_TOOLS_HOME for host tools and don't
unconditionally set TOOLCHAIN_HOME, preventing the detection of
llvm/clang host toolchain.

Signed-off-by: Oleg Zhurakivskyy <[email protected]>

Author: ozhuraki

cmake/toolchain/zephyr/0.9.5/host-tools.cmake

@@ -1,16 +1,16 @@
 # SPDX-License-Identifier: Apache-2.0
 
 if(MINGW)
-  set(TOOLCHAIN_HOME ${ZEPHYR_SDK_INSTALL_DIR}/sysroots/i686-pokysdk-mingw32)
+  set(HOST_TOOLS_HOME ${ZEPHYR_SDK_INSTALL_DIR}/sysroots/i686-pokysdk-mingw32)
 else()
-  set(TOOLCHAIN_HOME ${ZEPHYR_SDK_INSTALL_DIR}/sysroots/${TOOLCHAIN_ARCH}-pokysdk-linux)
+  set(HOST_TOOLS_HOME ${ZEPHYR_SDK_INSTALL_DIR}/sysroots/${TOOLCHAIN_ARCH}-pokysdk-linux)
 endif()
 
 # Path used for searching by the find_*() functions, with appropriate
 # suffixes added. Ensures that the SDK's host tools will be found when
 # we call, e.g. find_program(QEMU qemu-system-x86)
-list(APPEND CMAKE_PREFIX_PATH ${TOOLCHAIN_HOME}/usr)
+list(APPEND CMAKE_PREFIX_PATH ${HOST_TOOLS_HOME}/usr)
 
 # TODO: Use find_* somehow for these as well?
-set_ifndef(QEMU_BIOS            ${TOOLCHAIN_HOME}/usr/share/qemu)
-set_ifndef(OPENOCD_DEFAULT_PATH ${TOOLCHAIN_HOME}/usr/share/openocd/scripts)
+set_ifndef(QEMU_BIOS            ${HOST_TOOLS_HOME}/usr/share/qemu)
+set_ifndef(OPENOCD_DEFAULT_PATH ${HOST_TOOLS_HOME}/usr/share/openocd/scripts)