Fix nano-malloc build

The nano malloc build broke with:
  Commit 357d7fcc6
  In <stdio.h> provide only necessary types

The above commit exposed a latent missing-header bug:
  newlib/libc/stdlib/nano-mallocr.c:220:33: error: ‘uintptr_t’ undeclared (first use in this function)

Fix by including <stdint.h>.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>

newlib/libc/stdlib/nano-mallocr.c

@@ -36,6 +36,7 @@
 #include <string.h>
 #include <errno.h>
 #include <malloc.h>
+#include <stdint.h>
 
 #if DEBUG
 #include <assert.h>