libbpf's hashmap use of __WORDSIZE

[Arnaldo Carvalho de Melo]

Hi Andrii,

	We've got that hashmap.[ch] copy from libbpf so that we can
build perf in systems where libbpf isn't available, and to make it build
in all the containers I regularly test build perf I had to add the patch
below, I test build with many versions of both gcc and clang and
multiple libcs.

  https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html

The way that tools/include/linux/bitops.h has been doing since 2012 is
explained in:

  http://git.kernel.org/torvalds/c/3f34f6c0233ae055b5

Please take a look and see if you find it acceptable,

Thanks,

- Arnaldo
  
  Warning: Kernel ABI header at 'tools/perf/util/hashmap.h' differs from latest version at 'tools/lib/bpf/hashmap.h'
  diff -u tools/perf/util/hashmap.h tools/lib/bpf/hashmap.h

$ diff -u tools/lib/bpf/hashmap.h tools/perf/util/hashmap.h
--- tools/lib/bpf/hashmap.h	2020-06-05 13:25:27.822079838 -0300
+++ tools/perf/util/hashmap.h	2020-06-05 13:25:27.838079794 -0300
@@ -10,10 +10,9 @@
 
 #include <stdbool.h>
 #include <stddef.h>
-#ifdef __GLIBC__
-#include <bits/wordsize.h>
-#else
-#include <bits/reg.h>
+#include <limits.h>
+#ifndef __WORDSIZE
+#define __WORDSIZE (__SIZEOF_LONG__ * 8)
 #endif
 
 static inline size_t hash_bits(size_t h, int bits)