Update testgenerator to generate #includes instead of hard-coded

declarations.

Its output now matches the managed tests that were updated by the other
script.

Author: mattmccutchen-cci

clang/test/3C/testgenerator.py

@@ -51,20 +51,9 @@
 # header that should top every file
 header = """\
 #include <stddef.h>
-extern _Itype_for_any(T) void *calloc(size_t nmemb, size_t size)
-    : itype(_Array_ptr<T>) byte_count(nmemb * size);
-extern _Itype_for_any(T) void free(void *pointer
-                                   : itype(_Array_ptr<T>) byte_count(0));
-extern _Itype_for_any(T) void *malloc(size_t size)
-    : itype(_Array_ptr<T>) byte_count(size);
-extern _Itype_for_any(T) void *realloc(void *pointer
-                                       : itype(_Array_ptr<T>) byte_count(1),
-                                         size_t size)
-    : itype(_Array_ptr<T>) byte_count(size);
-extern _Unchecked int printf(const char *restrict format
-                  : itype(restrict _Nt_array_ptr<const char>), ...);
-extern _Unchecked char *strcpy(char *restrict dest, const char *restrict src
-                               : itype(restrict _Nt_array_ptr<const char>));
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
 """
 
 # miscallaneous struct definitions that may or may not be used by the files