conformtest: use proper _POSIX_C_SOURCE value for POSIX.

The conform/ tests were using -D_POSIX_C_SOURCE=199912 to test "POSIX"
(1995/6).  This patch changes them to use 199506L, the proper value
from the relevant edition of POSIX.  (This doesn't make any difference
to features.h, but is the logically correct value to use.)  Tested for
x86_64.

	* conform/GlibcConform.pm ($CFLAGS{"POSIX"}): Use
	-D_POSIX_C_SOURCE=199506L.

ChangeLog

@@ -1,5 +1,8 @@
 2015-05-20  Joseph Myers  <joseph@codesourcery.com>
 
+	* conform/GlibcConform.pm ($CFLAGS{"POSIX"}): Use
+	-D_POSIX_C_SOURCE=199506L.
+
 	* conform/data/locale.h-data [POSIX] (LC_MESSAGES): Require.
 
 	* conform/data/unistd.h-data (_POSIX_VERSION): Require.

conform/GlibcConform.pm

@@ -28,7 +28,7 @@ require Exporter;
 $CFLAGS{"ISO"} = "-ansi";
 $CFLAGS{"ISO99"} = "-std=c99";
 $CFLAGS{"ISO11"} = "-std=c1x -D_ISOC11_SOURCE";
-$CFLAGS{"POSIX"} = "-D_POSIX_C_SOURCE=199912 -ansi";
+$CFLAGS{"POSIX"} = "-D_POSIX_C_SOURCE=199506L -ansi";
 $CFLAGS{"XPG3"} = "-ansi -D_XOPEN_SOURCE";
 $CFLAGS{"XPG4"} = "-ansi -D_XOPEN_SOURCE -D_XOPEN_SOURCE_EXTENDED";
 $CFLAGS{"UNIX98"} = "-ansi -D_XOPEN_SOURCE=500";