Issue #12852: Set _POSIX_C_SOURCE to 200809 to get POSIX 2008

configure.in: Set _POSIX_C_SOURCE to 200809L, instead of 200112L, to activate
features from IEEE Stds 1003.1-2008.
diff --git a/configure.in b/configure.in
index f9be64a..800ba26 100644
--- a/configure.in
+++ b/configure.in
@@ -408,8 +408,7 @@
   AC_DEFINE(_XOPEN_SOURCE_EXTENDED, 1,
    	    Define to activate Unix95-and-earlier features)
 
-  AC_DEFINE(_POSIX_C_SOURCE, 200112L, Define to activate features from IEEE Stds 1003.1-2001)
-  
+  AC_DEFINE(_POSIX_C_SOURCE, 200809L, Define to activate features from IEEE Stds 1003.1-2008)
 fi
 
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