Using _POSIX_C_SOURCE in the middle of a header is incorrect and may work...

Using _POSIX_C_SOURCE in the middle of a header is incorrect and may work unreliably because of multiple-include guards

src/tsearch.h

@@ -20,7 +20,6 @@ void *tfind(const void *vkey, void * const *vrootp,
             int (*compar)(const void *, const void *));
 
 #else
-#define _POSIX_C_SOURCE 200809L
 #include <search.h>
 #endif