Add support for building on Windows using MSYS2/UCRT64.

Author: hydra

Makefile

@@ -67,13 +67,17 @@ all : check_tools bootloaders
 
 # Check if tools are installed
 check_tools:
+ifeq ($(MSYSTEM),UCRT64)
+	@$(SHELL) -c 'command -v $(CC) >/dev/null 2>&1 || { echo "Error: please install tools first with target arm_sdk_install."; exit 1; }'
+else
 ifeq ($(OS),Windows_NT)
 	@if not exist "$(CC).exe" ( \
 		echo Error: please install tools first with target arm_sdk_install. & exit /B 1 \
 	)
 else
 	@$(SHELL) -c 'command -v $(CC) >/dev/null 2>&1 || { echo "Error: please install tools first with target arm_sdk_install."; exit 1; }'
 endif
+endif
 
 clean :
 	@echo Removing $(OBJ) directory

make/tools.mk

@@ -4,6 +4,17 @@
 #
 ###############################################################
 
+ifeq ($(MSYSTEM),UCRT64)
+OSDIR:=windows
+ARM_SDK_PREFIX:=tools/windows/xpack-arm-none-eabi-gcc-10.3.1-2.3/bin/arm-none-eabi-
+CP:=cp
+DSEP:=/
+NUL:=/dev/null
+MKDIR:=mkdir
+RM:=rm
+CUT:=cut
+FGREP:=fgrep
+else
 
 ifeq ($(OS),Windows_NT)
 OSDIR:=windows
@@ -45,6 +56,7 @@ CUT:=cut
 FGREP:=fgrep
 endif
 endif
+endif
 
 # workaround for lack of a lowercase function in GNU make
 # look away before this sends you blind ....