Fix optimisation flags, so delay_ms works

CMakeLists.txt

@@ -117,15 +117,12 @@ message(STATUS "Set CMAKE_SYSTEM_LIBRARY_PATH to ${CMAKE_SYSTEM_LIBRARY_PATH}")
 ##################################################################################
 set(CSTANDARD "")
 set(CDEBUG    "")
-set(CWARN     "-Wall -Wextra -Wno-main -Wstrict-overflow=5 -Winline")
-set(CTUNING   "-fstrict-overflow -fno-strict-aliasing")
-set(COPT      "-Os")
-set(CMCU      "-mmcu=${MCU}")
-#set(CDEFS     "-DF_CPU=${F_CPU}") Have to set this using the line below otherwise we get errors about not defining F_CPU
-add_definitions(-DF_CPU=${F_CPU})
-
-set(CMAKE_C_CFLAGS "${CMCU} ${CDEBUG} ${CDEFS} ${COPT} ${CWARN} ${CSTANDARD} ${CTUNING}")
+set(CWARN     -Wall -Wextra -Wno-main -Wstrict-overflow=5 -Winline)
+set(CTUNING   -fstrict-overflow -fno-strict-aliasing)
+set(COPT      -Os)
 
+add_definitions(-DF_CPU=${F_CPU})
+add_compile_options(${CDEBUG} ${COPT} ${CWARN} ${CSTANDARD} ${CTUNING})
 
 
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