build/printf: fix incorrect format specifiers

build/printf: fix incorrect format specifiers

The following incorrect format specifiers and incorrect number of parameters
passed to printf like functions are reported by clang:

mce.c:601:18: error: data argument not used by format string [-Werror,-Wformat-extra-args]
                 smp_processor_id());
                 ^

xenpm.c:102:23: error: data argument not used by format string [-Werror,-Wformat-extra-args]
                what, argv[argc > 1]);
                      ^

libxl_internal.c:25:69: error: data argument not used by format string
      [-Werror,-Wformat-extra-args]
    libxl__log(ctx, XTL_CRITICAL, ENOMEM, 0,0, func, INVALID_DOMID, L);
                                                                    ^
libxl_internal.c:24:17: note: expanded from macro 'L'
          func, (unsigned long)nmemb, (unsigned long)size
                ^
libxl_internal.c:26:21: error: data argument not used by format string
      [-Werror,-Wformat-extra-args]
    fprintf(stderr, L);
                    ^
libxl_internal.c:24:17: note: expanded from macro 'L'
          func, (unsigned long)nmemb, (unsigned long)size
                ^

This patch contains the fixes for them and enables -Wformat for clang.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>