Implement Late Externalization for STRONG externalization type

[giulianobelinassi]

Take the following code as example:

\#include <stdio.h>
int main(void) {
  printf("Hello, world\n");
  return 0;
}

And assume we want to strongly externalize the function printf. The resulting code would be:

\#define _STDIO_H	1
\#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
\#include <bits/libc-header-start.h>
\#define __need_size_t
\#define __need_NULL
\#include <stddef.h>
\#define __need___va_list
\#include <stdarg.h>
\#include <bits/types.h>
\#include <bits/types/__fpos_t.h>
\#include <bits/types/__fpos64_t.h>
\#include <bits/types/__FILE.h>
\#include <bits/types/FILE.h>
\#include <bits/types/struct_FILE.h>
\# include <bits/types/cookie_io_functions_t.h>
\#define L_tmpnam 20
\#include <bits/stdio_lim.h>
\#define __attr_dealloc_fclose __attr_dealloc (fclose, 1)
/** clang-extract: from /usr/include/stdio.h:361:1  */
static int (*klpe_printf)(const char *restrict, ...);

\#include <bits/floatn.h>
/** clang-extract: from /tmp/rewrite-3.c:5:1  */
int main(void)
{
  (*klpe_printf)("Hello, world!\n");
  return 0;
}

Clearly, those headers and defines could be avoided. For example, this would be perfectly valid:

\#include <stdio.h>
/** clang-extract: from /tmp/rewrite-3.c:5:1  */
static int (*klpe_printf)(const char *restrict, ...);

/** clang-extract: from /tmp/rewrite-3.c:4:1  */
int main(void)
{
  (*klpe_printf)("Hello, world!\n");
  return 0;
}

Because the definition of klpe_printf is located right before its first use. This commit does this by computing a possible place where the externalized variable can be output just before the first use, hence we externalize the variable later than the original code would suggest.

To enable this option, the user must pass -DCE_LATE_EXTERNALIZE to clang-extract.

[marcosps]

Maybe array as argument name could be improved? I mean, when looking at the code, the name array doesn't say much about what is containers.