[2.27 COMMITTED] manual: Update the _ISOC99_SOURCE description.

[Dmitry V. Levin]

From: Rical Jasan <ricaljasan@pacific.net>

The current description refers to ISO C99 not being widely adopted,
which it is believed to be now.

	* manual/creature.texi (_ISOC99_SOURCE): Update the dated
	description.

(cherry picked from commit e8d190b9ed81a1b342f0969bc2b5505403183bce)
---
 ChangeLog            | 3 +++
 manual/creature.texi | 7 +++----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 911e090..e158364 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2018-02-20  Rical Jasan  <ricaljasan@pacific.net>
 
+	* manual/creature.texi (_ISOC99_SOURCE): Update the dated
+	description.
+
 	[BZ #16335]
 	* manual/creature.texi (_POSIX_C_SOURCE): Document special values
 	of 199606L, 200112L, and 200809L.
diff --git a/manual/creature.texi b/manual/creature.texi
index 483bf85..fe7a779 100644
--- a/manual/creature.texi
+++ b/manual/creature.texi
@@ -167,10 +167,9 @@ This macro was introduced as part of the Large File Support extension
 
 @defvr Macro _ISOC99_SOURCE
 @standards{GNU, (none)}
-Until the revised @w{ISO C} standard is widely adopted the new features
-are not automatically enabled.  @Theglibc{} nevertheless has a complete
-implementation of the new standard and to enable the new features the
-macro @code{_ISOC99_SOURCE} should be defined.
+If this macro is defined, features from ISO C99 are included.  Since
+these features are included by default, this macro is mostly relevant
+when the compiler uses an earlier language version.
 @end defvr
 
 @defvr Macro _ISOC11_SOURCE
-- 
ldv