Feature test macros overhaul: dirent.h

MAXNAMLEN is a BSDism.

Use the proper internal macros instead of !_POSIX_SOURCE.  telldir and
seekdir are XSI, scandir and alphasort are POSIX.1-2008, and scandirat
is GNU.

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

newlib/libc/include/dirent.h

@@ -3,9 +3,10 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
+#include <sys/cdefs.h>
 #include <sys/dirent.h>
 
-#if !defined(MAXNAMLEN) && !defined(_POSIX_SOURCE)
+#if !defined(MAXNAMLEN) && __BSD_VISIBLE
 #define MAXNAMLEN 1024
 #endif