* Avoid making all warnings into errors
* Extra optimizations via COPT should be overwritable 

--- mpy-cross/Makefile.orig	2021-09-01 14:07:13 UTC
+++ mpy-cross/Makefile
@@ -17,7 +17,7 @@ INC += -I$(BUILD)
 INC += -I$(TOP)
 
 # compiler settings
-CWARN = -Wall -Werror
+CWARN = -Wall
 CWARN += -Wextra -Wno-unused-parameter -Wpointer-arith
 CFLAGS = $(INC) $(CWARN) -std=gnu99 $(CFLAGS_MOD) $(COPT) $(CFLAGS_EXTRA)
 CFLAGS += -fdata-sections -ffunction-sections -fno-asynchronous-unwind-tables
@@ -25,9 +25,9 @@ CFLAGS += -fdata-sections -ffunction-sections -fno-asy
 # Debugging/Optimization
 ifdef DEBUG
 CFLAGS += -g
-COPT = -O0
+COPT ?= -O0
 else
-COPT = -Os #-DNDEBUG
+COPT ?= -Os #-DNDEBUG
 endif
 
 # On OSX, 'gcc' is a symlink to clang unless a real gcc is installed.