tools headers UAPI: Sync linux/const.h with the kernel headers

To pick up the changes in:

  947697c ("uapi: Define GENMASK_U128")

That causes no changes in tooling, just addresses this perf build
warning:

  Warning: Kernel ABI header differences:
    diff -u tools/include/uapi/linux/const.h include/uapi/linux/const.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Link: https://lore.kernel.org/lkml/ZwltGNJwujKu1Fgn@x1
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: acmel

tools/include/uapi/linux/const.h

@@ -28,6 +28,23 @@
 #define _BITUL(x)	(_UL(1) << (x))
 #define _BITULL(x)	(_ULL(1) << (x))
 
+#if !defined(__ASSEMBLY__)
+/*
+ * Missing asm support
+ *
+ * __BIT128() would not work in the asm code, as it shifts an
+ * 'unsigned __init128' data type as direct representation of
+ * 128 bit constants is not supported in the gcc compiler, as
+ * they get silently truncated.
+ *
+ * TODO: Please revisit this implementation when gcc compiler
+ * starts representing 128 bit constants directly like long
+ * and unsigned long etc. Subsequently drop the comment for
+ * GENMASK_U128() which would then start supporting asm code.
+ */
+#define _BIT128(x)	((unsigned __int128)(1) << (x))
+#endif
+
 #define __ALIGN_KERNEL(x, a)		__ALIGN_KERNEL_MASK(x, (__typeof__(x))(a) - 1)
 #define __ALIGN_KERNEL_MASK(x, mask)	(((x) + (mask)) & ~(mask))