cmake: Support both toolchain directory layouts

Until zephyrproject-rtos/sdk-ng#936 is merged,
SDK 0.18 is incompatible with previous versions as the paths to
find the cmake bits is different.

Deal with that by checking for files in the wrong place as well as the
right one.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

cmake/toolchain/zephyr/generic.cmake

@@ -2,7 +2,11 @@
 
 if(TOOLCHAIN_VARIANT_COMPILER STREQUAL "gnu" OR
     NOT DEFINED TOOLCHAIN_VARIANT_COMPILER)
-  include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/generic.cmake)
+  if(EXISTS ${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/generic.cmake)
+    include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/generic.cmake)
+  else()
+    include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/generic.cmake)
+  endif()
   set(TOOLCHAIN_VARIANT_COMPILER "gnu" CACHE STRING "compiler used by the toolchain variant" FORCE)
 
   set(TOOLCHAIN_KCONFIG_DIR ${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr)

cmake/toolchain/zephyr/target.cmake

@@ -3,7 +3,11 @@
 if(TOOLCHAIN_VARIANT_COMPILER STREQUAL "gnu" OR
    TOOLCHAIN_VARIANT_COMPILER STREQUAL "default")
   set(TOOLCHAIN_VARIANT_COMPILER gnu CACHE STRING "Variant compiler being used")
-  include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/target.cmake)
+  if(EXISTS ${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/target.cmake)
+    include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/gnu/target.cmake)
+  else()
+    include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/target.cmake)
+  endif()
 elseif (TOOLCHAIN_VARIANT_COMPILER STREQUAL "llvm")
   set(TOOLCHAIN_VARIANT_COMPILER llvm CACHE STRING "Variant compiler being used")
   include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/llvm/target.cmake)