fcntl.h: O_SEARCH was missing for powerpc

put some macros that do not differ between architectures in the
main header and remove from bits.
restructure mips header so it has the same structure as the others.

include/fcntl.h

@@ -37,6 +37,10 @@ int openat(int, const char *, int, ...);
 int posix_fadvise(int, off_t, off_t, int);
 int posix_fallocate(int, off_t, off_t);
 
+#define O_SEARCH  010000000
+#define O_EXEC    010000000
+#define O_PATH    010000000
+
 #define O_ACCMODE (03|O_SEARCH)
 #define O_RDONLY  00
 #define O_WRONLY  01