Support for cmake < 3.6.

cmake/gcc_stm32.cmake

@@ -44,9 +44,15 @@ ELSE()
     SET(TOOL_EXECUTABLE_SUFFIX "")
 ENDIF()
 
-SET(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
-SET(CMAKE_C_COMPILER ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-gcc${TOOL_EXECUTABLE_SUFFIX})
-SET(CMAKE_CXX_COMPILER ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-g++${TOOL_EXECUTABLE_SUFFIX})
+IF(${CMAKE_VERSION} VERSION_LESS 3.6.0)
+    INCLUDE(CMakeForceCompiler)
+    CMAKE_FORCE_C_COMPILER(${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-gcc${TOOL_EXECUTABLE_SUFFIX} GNU)
+    CMAKE_FORCE_CXX_COMPILER(${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-g++${TOOL_EXECUTABLE_SUFFIX} GNU)
+ELSE()
+    SET(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+    SET(CMAKE_C_COMPILER ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-gcc${TOOL_EXECUTABLE_SUFFIX})
+    SET(CMAKE_CXX_COMPILER ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-g++${TOOL_EXECUTABLE_SUFFIX})
+ENDIF()
 SET(CMAKE_ASM_COMPILER ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-gcc${TOOL_EXECUTABLE_SUFFIX})
 
 SET(CMAKE_OBJCOPY ${TOOLCHAIN_BIN_DIR}/${TARGET_TRIPLET}-objcopy${TOOL_EXECUTABLE_SUFFIX} CACHE INTERNAL "objcopy tool")