Apply all source related changes for the new INSTALL.md in one commit.

For people who want to have dkPless builds in their repo.

tools/gbafix/Makefile

@@ -3,10 +3,16 @@ CC ?= gcc
 
 SRCS = gbafix.c
 
-all: gbafix
+ifeq ($(OS),Windows_NT)
+EXE := .exe
+else
+EXE :=
+endif
+
+all: gbafix$(EXE)
 	@:
 
-gbafix: $(SRCS)
+gbafix$(EXE): $(SRCS)
 	$(CC) $(SRCS) -o $@ $(LDFLAGS)
 
 clean: