Fix mingw-w64 build and cross-compilation

Makefile

@@ -3,12 +3,18 @@ OS:=$(shell uname -s)
 endif
 
 ifeq ($(OS),Windows)
+ifndef SDL2_PREFIX
+SDL2_PREFIX:="C:/MinGW/usr"
+endif
+ifndef GLEW32S_LIB
+GLEW32S_LIB=glew32s.lib
+endif
 
 MEM:=mem_win.o
 BLASTEM:=blastem.exe
 CC:=wine gcc.exe
-CFLAGS:=-O2 -std=gnu99 -Wreturn-type -Werror=return-type -Werror=implicit-function-declaration -I"C:/MinGW/usr/include/SDL2" -DGLEW_STATIC
-LDFLAGS:= -L"C:/MinGW/usr/lib" -lm -lmingw32 -lSDL2main -lSDL2 -lopengl32 -lglu32 -mwindows
+CFLAGS:=-O2 -std=gnu99 -Wreturn-type -Werror=return-type -Werror=implicit-function-declaration -I"$(SDL2_PREFIX)/include/SDL2" -DGLEW_STATIC
+LDFLAGS:= $(GLEW32S_LIB) -L"$(SDL2_PREFIX)/lib" -lm -lmingw32 -lSDL2main -lSDL2 -lopengl32 -lglu32 -mwindows
 CPU:=i686
 
 else
@@ -117,11 +123,7 @@ else
 MAINOBJS+= $(Z80OBJS)
 endif
 
-ifeq ($(OS),Windows)
-MAINOBJS+= glew32s.lib
-endif
-
-all : dis zdis stateview vgmplay blastem
+all : dis zdis stateview vgmplay $(BLASTEM)
 
 $(BLASTEM) : $(MAINOBJS)
 	$(CC) -o $(BLASTEM) $(MAINOBJS) $(LDFLAGS)

config.c

@@ -9,7 +9,13 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef _WIN32
+#ifdef __MINGW64_VERSION_MAJOR
+#define MINGW_W64_VERSION (__MINGW64_VERSION_MAJOR * 1000 + __MINGW64_VERSION_MINOR)
+#else
+#define MINGW_W64_VERSION 0
+#endif
+
+#if defined(_WIN32) && (MINGW_W64_VERSION < 3003)
 char * strtok_r(char * input, char * sep, char ** state)
 {
 	if (input) {

mem_win.c

@@ -5,7 +5,7 @@
 */
 
 #include "mem.h"
-#include <Windows.h>
+#include <windows.h>
 
 void * alloc_code(size_t *size)
 {

util.c

@@ -87,8 +87,8 @@ void set_exe_str(char * str)
 }
 
 #ifdef _WIN32
-#include "Shlobj.h"
-#include "Windows.h"
+#include <windows.h>
+#include <shlobj.h>
 
 char * get_home_dir()
 {