py: Add win32-specific header for alloca().
diff --git a/py/builtinimport.c b/py/builtinimport.c
index 262ee04..4a2f651 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -3,6 +3,10 @@
 #include <stdio.h>
 #include <string.h>
 #include <assert.h>
+#ifdef __MINGW32__
+// For alloca()
+#include <malloc.h>
+#endif
 
 #include "nlr.h"
 #include "misc.h"