fix multiple minor namespace issues in headers

fcntl.h: AT_* is not a reserved namespace so extensions cannot be
exposed by default.

langinfo.h: YESSTR and NOSTR were removed from the standard.

limits.h: NL_NMAX was removed from the standard.

signal.h: the conditional for NSIG was wrongly checking _XOPEN_SOURCE
rather than _BSD_SOURCE. this was purely a mistake; it doesn't even
match the commit message from the commit that added it.

include/fcntl.h

@@ -59,8 +59,6 @@ int posix_fallocate(int, off_t, off_t);
 #define AT_REMOVEDIR 0x200
 #define AT_SYMLINK_FOLLOW 0x400
 #define AT_EACCESS 0x200
-#define AT_NO_AUTOMOUNT 0x800
-#define AT_EMPTY_PATH 0x1000
 
 #define POSIX_FADV_NORMAL     0
 #define POSIX_FADV_RANDOM     1
@@ -95,6 +93,9 @@ int posix_fallocate(int, off_t, off_t);
 #endif
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#define AT_NO_AUTOMOUNT 0x800
+#define AT_EMPTY_PATH 0x1000
+
 #define FAPPEND O_APPEND
 #define FFSYNC O_FSYNC
 #define FASYNC O_ASYNC

include/langinfo.h

@@ -5,6 +5,7 @@
 extern "C" {
 #endif
 
+#include <features.h>
 #include <nl_types.h>
 
 #define __NEED_locale_t
@@ -75,8 +76,11 @@ extern "C" {
 #define THOUSEP 0x10001
 #define YESEXPR 0x50000
 #define NOEXPR 0x50001
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #define YESSTR 0x50002
 #define NOSTR 0x50003
+#endif
 
 char *nl_langinfo(nl_item);
 char *nl_langinfo_l(nl_item, locale_t);

include/limits.h

@@ -84,12 +84,18 @@
 #define NL_ARGMAX 9
 #define NL_LANGMAX 32
 #define NL_MSGMAX 32767
-#define NL_NMAX (MB_LEN_MAX*4)
 #define NL_SETMAX 255
 #define NL_TEXTMAX 2048
 
 #endif
 
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE) \
+ || (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE+0 < 700)
+
+#define NL_NMAX 16
+
+#endif
+
 /* POSIX/SUS requirements follow. These numbers come directly
  * from SUS and have nothing to do with the host system. */
 

include/signal.h

@@ -218,11 +218,8 @@ void (*sigset(int, void (*)(int)))(int);
 #define SIGSTKSZ 8192
 #endif
 
-#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)
-#define NSIG _NSIG
-#endif
-
 #if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
+#define NSIG _NSIG
 typedef void (*sig_t)(int);
 #endif