Don't claim GCC predefines __POSIX__

[Joseph S. Myers]

Bug 4596 notes that the claim in the manual that GCC predefines
__POSIX__ on POSIX systems is wrong.  Thus, I propose this patch to
remove that claim (not mentioning the #system(posix) alternative since
GCC preprocessor assertions are deprecated).

2012-02-17  Joseph Myers  <joseph@codesourcery.com>

	[BZ #4596]
	* manual/conf.texi (_POSIX_VERSION): Do not mention __POSIX__.

diff --git a/manual/conf.texi b/manual/conf.texi
index 605e305..30499d9 100644
--- a/manual/conf.texi
+++ b/manual/conf.texi
@@ -248,11 +248,6 @@ by including @file{unistd.h} and then checking whether
 probably fail because there is no @file{unistd.h}.  We do not know of
 @emph{any} way you can reliably test at compilation time whether your
 target system supports POSIX or whether @file{unistd.h} exists.
-
-The GNU C compiler predefines the symbol @code{__POSIX__} if the target
-system is a POSIX system.  Provided you do not use any other compilers
-on POSIX systems, testing @code{defined (__POSIX__)} will reliably
-detect such systems.
 @end deftypevr
 
 @comment unistd.h

-- 
Joseph S. Myers
joseph@codesourcery.com