fix regressions in app compatibility from previous sys/ipc.h changes

despite glibc using __key and __seq rather than key and seq, some
applications, notably busybox, assume the names are key and seq unless
glibc is being used. and the names key and seq are really the ones
that _should_ be exposed when not attempting to present a
standards-conforming namespace; apps should not be using names that
begin with double-underscore. thus, the optimal fix is to use key and
seq as the actual names of the members when in bsd/gnu source profile,
and define macros for __key and __seq that redirect to plain key and
seq.

include/sys/ipc.h

@@ -16,6 +16,11 @@ extern "C" {
 #define __ipc_perm_key __key
 #define __ipc_perm_seq __seq
 
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#define __key key
+#define __seq seq
+#endif
+
 #include <bits/ipc.h>
 
 #define IPC_CREAT  01000