Make it possible to build SameBoy for Windows while linking against Windows' msvct.dll

Makefile

@@ -322,6 +322,13 @@ CFLAGS += -Wno-deprecated-declarations
 ifeq ($(PLATFORM),windows32)
 CFLAGS += -Wno-deprecated-declarations # Seems like Microsoft deprecated every single LIBC function
 LDFLAGS += -Wl,/NODEFAULTLIB:libcmt.lib
+
+ifneq ($(USE_MSVCRT_DLL),)
+CFLAGS += -D_NO_CRT_STDIO_INLINE -DUSE_MSVCRT_DLL
+$(BIN)/SDL/sameboy.exe: $(OBJ)/Windows/msvcrt.lib
+$(BIN)/SDL/sameboy_debugger.exe: $(OBJ)/Windows/msvcrt.lib
+endif
+
 endif
 endif
 
@@ -894,6 +901,10 @@ $(INC)/%.h: Core/%.h
 	-@$(MKDIR) -p $(dir $@)
 	sed "s/'/@SINGLE_QUOTE@/g" $^ | cppp $(CPPP_FLAGS) | sed "s/@SINGLE_QUOTE@/'/g" > $@
 	
+# Generate msvcrt.lib so we can use the always-present msvcrt.dll
+$(OBJ)/Windows/msvcrt.lib: Windows/msvcrt.def
+	lib.exe /MACHINE:X64 /def:$< /out:$@
+	
 # Clean
 clean:
 	rm -rf build

Windows/crt.c

@@ -0,0 +1,91 @@
+#include <windows.h>
+#include <stdio.h>
+
+#ifdef USE_MSVCRT_DLL
+/* Stub-out functions imported by VS's msvcrt.lib but are not implemented in msvcrt.dll */
+
+/* We don't use exceptions, these are used by the uncaught exception handler and can be replaced with aborts */
+
+void *__current_exception(void)
+{
+    abort();
+    return NULL;
+}
+
+void *__current_exception_context(void)
+{
+    abort();
+    return NULL;
+}
+
+/* terminate uses a mangled symbol on msvcrt.dll */
+
+void msvcrt_terminate(void) __asm__("?terminate@@YAXXZ");
+void terminate(void)
+{
+    msvcrt_terminate();
+}
+
+/* We need to redirect these to msvcrt.dll's atexit */
+
+int _crt_atexit(void (*function)(void))
+{
+    return ((typeof(atexit) *)GetProcAddress(GetModuleHandleA("msvcrt.dll"), "atexit"))(function);
+}
+
+int _register_onexit_function(void *table, void (*function)(void))
+{
+    return ((typeof(atexit) *)GetProcAddress(GetModuleHandleA("msvcrt.dll"), "atexit"))(function);
+}
+
+/* Various imported function we don't need and can nop-out */
+
+int *__p__commode(void)
+{
+    static int dummy;
+    return &dummy;
+}
+
+int _configthreadlocale(int flag)
+{
+    return 0;
+}
+
+errno_t _configure_narrow_argv(unsigned mode)
+{
+    return 0;
+}
+
+char *_get_narrow_winmain_command_line(void)
+{
+    return NULL;
+}
+
+int _initialize_narrow_environment()
+{
+    return 0;
+}
+
+int _initialize_onexit_table(void *table)
+{
+    return 0;
+}
+
+void _register_thread_local_exe_atexit_callback(const void *callback)
+{
+}
+
+int _seh_filter_exe(unsigned exception_num, void *exception)
+{
+    return 0;
+}
+
+void _set_app_type(unsigned type)
+{
+}
+
+int _set_new_mode(int new_mode)
+{
+    return 0;
+}
+#endif

Windows/math.c

@@ -0,0 +1,18 @@
+#include <math.h>
+
+#ifdef USE_MSVCRT_DLL
+
+/* "Old" (Pre-2015) Windows headers/libc don't have round and exp2. */
+
+__attribute__((no_builtin)) double round(double f)
+{
+    return f >= 0? (int)(f + 0.5) : (int)(f - 0.5);
+}
+
+
+__attribute__((no_builtin)) double exp2(double f)
+{
+    return pow(2, f);
+}
+
+#endif

Windows/math.h

@@ -1,9 +0,0 @@
-#pragma once
-#include_next <math.h>
-#ifndef __MINGW32__
-/* "Old" (Pre-2015) Windows headers/libc don't have round. */
-static inline double round(double f)
-{
-    return f >= 0? (int)(f + 0.5) : (int)(f - 0.5);
-}
-#endif

Windows/stdio.c

@@ -0,0 +1,14 @@
+#include <stdio.h>
+#include <unistd.h>
+
+#ifdef USE_MSVCRT_DLL
+
+FILE *__acrt_iob_func(unsigned index)
+{
+    static FILE *files[3];
+    if (index > sizeof(files) / sizeof(files[0])) return NULL;
+    if (files[index]) return files[index];
+    return (files[index] = fdopen(index, index == STDIN_FILENO? "r" : "w"));
+}
+
+#endif