Add WORD_BITS predef detection.

fixes https://github.com/boostorg/predef/pull/107
fixes https://github.com/boostorg/predef/pull/108

include/boost/predef/other/endian.h

@@ -95,7 +95,7 @@ information and acquired knowledge:
 #   endif
 #endif
 
-/* Built-in byte-swpped big-endian macros.
+/* Built-in byte-swapped big-endian macros.
  */
 #if !BOOST_ENDIAN_BIG_BYTE && !BOOST_ENDIAN_BIG_WORD && \
     !BOOST_ENDIAN_LITTLE_BYTE && !BOOST_ENDIAN_LITTLE_WORD
@@ -112,7 +112,7 @@ information and acquired knowledge:
 #   endif
 #endif
 
-/* Built-in byte-swpped little-endian macros.
+/* Built-in byte-swapped little-endian macros.
  */
 #if !BOOST_ENDIAN_BIG_BYTE && !BOOST_ENDIAN_BIG_WORD && \
     !BOOST_ENDIAN_LITTLE_BYTE && !BOOST_ENDIAN_LITTLE_WORD
@@ -154,7 +154,7 @@ information and acquired knowledge:
 #endif
 
 /* Windows on ARM, if not otherwise detected/specified, is always
- * byte-swaped little-endian.
+ * byte-swapped little-endian.
  */
 #if !BOOST_ENDIAN_BIG_BYTE && !BOOST_ENDIAN_BIG_WORD && \
     !BOOST_ENDIAN_LITTLE_BYTE && !BOOST_ENDIAN_LITTLE_WORD

include/boost/predef/other/wordsize.h

@@ -0,0 +1,69 @@
+/*
+Copyright Rene Ferdinand Rivera Morell 2020
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE_1_0.txt or copy at
+http://www.boost.org/LICENSE_1_0.txt)
+*/
+
+#ifndef BOOST_PREDEF_OTHER_WORD_SIZE_H
+#define BOOST_PREDEF_OTHER_WORD_SIZE_H
+
+#include <boost/predef/architecture.h>
+#include <boost/predef/version_number.h>
+#include <boost/predef/make.h>
+
+/* tag::reference[]
+= `BOOST_ARCH_WORD_BITS`
+
+Detects the native word size, in bits, for the current architecture. There are
+two types of macros for this detection:
+
+* `BOOST_ARCH_WORD_BITS`, gives the number of word size bits
+  (16, 32, 64).
+* `BOOST_ARCH_WORD_BITS_16`, `BOOST_ARCH_WORD_BITS_32`, and
+  `BOOST_ARCH_WORD_BITS_64`, indicate when the given word size is
+  detected.
+
+They allow for both single checks and direct use of the size in code.
+
+NOTE: The word size is determined manually on each architecture. Hence use of
+the `wordsize.h` header will also include all the architecture headers.
+
+*/ // end::reference[]
+
+#ifndef BOOST_ARCH_WORD_BITS_16
+#	define BOOST_ARCH_WORD_BITS_16 BOOST_VERSION_NUMBER_NOT_AVAILABLE
+#else
+#	define BOOST_ARCH_WORD_BITS 16
+#endif
+
+#ifndef BOOST_ARCH_WORD_BITS_32
+#	define BOOST_ARCH_WORD_BITS_32 BOOST_VERSION_NUMBER_NOT_AVAILABLE
+#else
+#	define BOOST_ARCH_WORD_BITS 32
+#endif
+
+#ifndef BOOST_ARCH_WORD_BITS_64
+#	define BOOST_ARCH_WORD_BITS_64 BOOST_VERSION_NUMBER_NOT_AVAILABLE
+#else
+#	define BOOST_ARCH_WORD_BITS 64
+#endif
+
+#ifndef BOOST_ARCH_WORD_BITS
+#	define BOOST_ARCH_WORD_BITS 0
+#endif
+
+#define BOOST_ARCH_WORD_BITS_16_NAME "16-bit Word Size"
+#define BOOST_ARCH_WORD_BITS_32_NAME "32-bit Word Size"
+#define BOOST_ARCH_WORD_BITS_64_NAME "64-bit Word Size"
+
+#endif
+
+#include <boost/predef/detail/test.h>
+BOOST_PREDEF_DECLARE_TEST(BOOST_ARCH_WORD_BITS_16,BOOST_ARCH_WORD_BITS_16_NAME)
+
+#include <boost/predef/detail/test.h>
+BOOST_PREDEF_DECLARE_TEST(BOOST_ARCH_WORD_BITS_32,BOOST_ARCH_WORD_BITS_32_NAME)
+
+#include <boost/predef/detail/test.h>
+BOOST_PREDEF_DECLARE_TEST(BOOST_ARCH_WORD_BITS_64,BOOST_ARCH_WORD_BITS_64_NAME)