declare standard C functions 'nogil'

Cython/Includes/stdio.pxd

 cdef extern from "stdio.h":
     ctypedef struct FILE
-    int printf(char *format, ...)
-    int fprintf(FILE *stream, char *format, ...)
-    int sprintf(char *str, char *format, ...)
-    FILE *fopen(char *path, char *mode)
-    int fclose(FILE *strea)
+    int printf(char *format, ...) nogil
+    int fprintf(FILE *stream, char *format, ...) nogil
+    int sprintf(char *str, char *format, ...) nogil
+    FILE *fopen(char *path, char *mode) nogil
+    int fclose(FILE *strea) nogil
     cdef FILE *stdout
-    int scanf(char *format, ...)
+    int scanf(char *format, ...) nogil

Cython/Includes/stdlib.pxd

 
 cdef extern from "stdlib.h":
-    void free(void *ptr)
-    void *malloc(size_t size)
-    void *realloc(void *ptr, size_t size)
-    size_t strlen(char *s)
-    char *strcpy(char *dest, char *src)
+    void free(void *ptr) nogil
+    void *malloc(size_t size) nogil
+    void *realloc(void *ptr, size_t size) nogil
+    size_t strlen(char *s) nogil
+    char *strcpy(char *dest, char *src) nogil