src/Makefile: Use MinSizeRel build option.

This makes the build as small as possible.  And recent versions of
arm-none-eabi-g++ (eg 10.2) currently have a problem compiling Timer.cpp.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

src/Makefile

@@ -27,7 +27,7 @@ all: codal_build
 codal_cmake:
 	$(MKDIR) -p $(BUILD)
 	$(call CODAL_PATCH)
-	(cd $(BUILD) && cmake ../$(CODAL_DIR) -DCMAKE_BUILD_TYPE=RelWithDebInfo)
+	(cd $(BUILD) && cmake ../$(CODAL_DIR) -DCMAKE_BUILD_TYPE=MinSizeRel)
 	$(call CODAL_CLEAN)
 
 # Build the codal app and make the final HEX file