Add option to disable spawnv define (#301)

configure.ac

@@ -60,7 +60,15 @@ AS_CASE([$host],
 AC_SUBST([EXTRA_LDFLAGS])
 
 AS_CASE([$host],
-	[*mingw*], [CFLAGS="$CFLAGS -D_spawnv=spawnv"],
+	[*mingw*], 
+        [
+        #There is no real way to determine whether UCRT is used vs normal MINGW but one way is by checking a define in <windows.h>
+        #If we are in UCRT we do not want to set the spawnv define because it breaks the build
+        IS_UCRT=`echo '#include <windows.h>'| gcc -E -dM -  | grep -i _UCRT | xargs`
+        AS_IF([test "$IS_UCRT" == ""], [
+            CFLAGS="$CFLAGS -D_spawnv=spawnv"
+        ])
+    ],
 	[CFLAGS="$CFLAGS"])
 
 AC_ARG_VAR([LIB_FUZZING_ENGINE], [Location of prebuilt fuzzing engine library])