/Fe not /Fo.

zsnes/src/makefile.ms

@@ -374,7 +374,7 @@ ${OBJFIX}: $<
 endif
 ${PSR}: $<
 ifeq (${ENV},msvc)
-	cl /EHsc /Fo$@ parsegen.cpp
+	cl /EHsc /Fe$@ parsegen.cpp
 else
 ifeq (${ENV},dos)
 	gpp -O3 -o $@ parsegen.cpp

zsnes/src/parsegen.cpp

@@ -254,7 +254,7 @@ ssize_t enhanced_atoi(const char *str)
     out_stream.close();
 
 #ifndef __GNUC__ //MSVC
-    system("cl /Foeatio.exe eatio.c");
+    system("cl /Feeatio.exe eatio.c");
 #else
     system("gcc -o eatio.exe eatio.c -s");
 #endif