Cast __builtin_swap64 to uint64_t.

strace 4.19 causes clang to emit a questionable warning:

  external/strace/nlattr.c:254:35: error: format specifies type 'unsigned long' but the argument has type 'unsigned long long' [-Werror,-Wformat]
                tprintf("htobe64(%" PRIu64 ")", be64toh(num));
                                 ~~~            ^~~~~~~~~~~~
  bionic/libc/include/sys/endian.h:100:20: note: expanded from macro 'be64toh'
  #define be64toh(x) htobe64(x)
                     ^~~~~~~~~~
  bionic/libc/include/sys/endian.h:80:17: note: expanded from macro 'htobe64'
  #define htobe64 __swap64
                  ^
  bionic/libc/include/sys/endian.h:48:18: note: expanded from macro '__swap64'
  #define __swap64 __builtin_bswap64
                   ^

What's happened here is:

* be64toh is __builtin_bswap64

* PRIu64 is "lu"

* __builtin_bswap64 is internally declared a "ULLiULLi"

All of which leads to the `unsigned long` != `unsigned long long` complaint.

It seems like __builtin_bswap64 should be ULiULi on 64-bit architectures,
where `long` rather than `long long` is the natural way to refer to 64-bit
types, as evidenced by the "lu" for PRIu64.

As long as clang behaves like this, though, we can work around it with a cast.

Also clean up the other casts in the file, be more consistent about whether
these function-like macros are defined with an argument, and remove an
incorrect comment.

Bug: http://b/65495954
Test: ran tests, built strace 4.19 without warnings
Change-Id: I8e06d4bf71e95d62f556eab8661033e04d487e0d