gcc_stm32.cmake: added ability to specify additional search path

gcc_stm32.cmake

@@ -54,7 +54,7 @@ SET(CMAKE_CXX_FLAGS_RELEASE "-Os -flto" CACHE INTERNAL "cxx compiler flags relea
 SET(CMAKE_ASM_FLAGS_RELEASE "" CACHE INTERNAL "asm compiler flags release")
 SET(CMAKE_EXE_LINKER_FLAGS_RELESE "-flto" CACHE INTERNAL "linker flags release")
 
-SET(CMAKE_FIND_ROOT_PATH ${TOOLCHAIN_PREFIX}/${TARGET_TRIPLET})
+SET(CMAKE_FIND_ROOT_PATH ${TOOLCHAIN_PREFIX}/${TARGET_TRIPLET} ${EXTRA_FIND_PATH})
 SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)