Implement memmove() in the kernel.

kernel/kernel.c

@@ -162,6 +162,13 @@ void *memcpy(void *dest, const void *src, size_t n)
     return dest;
 }
 
+void *memmove(void *dest, const void *src, size_t n)
+{
+    memcpy(freemem, src, n);
+    memcpy(dest, freemem, n);
+    return dest;
+}
+
 size_t strlen(const char *s)
 {
     int len = 0;

kernel/kernel.h

@@ -84,6 +84,7 @@ FILE *stdin, *stdout, *stderr;
 /* string.h functions */
 void *memset(void *s, int c, size_t n);
 void *memcpy(void *dest, const void *src, size_t n);
+void *memmove(void *dest, const void *src, size_t n);
 size_t strlen(const char *s);
 int strcmp(const char *s1, const char *s2);
 int strcasecmp(const char *s1, const char *s2);