[phobos] Octal literals in druntime/src/core/sys/posix/

[Don Clugston]

I gets errors when building d_do_test. There are multiple errors in
each of these files, I've shown only one.

druntime/src/core/sys/posix/sys/wait.d(78): octal literals 0177 are
deprecated, use std.conv.octal!177 instead
druntime/src/core/sys/posix/fcntl.d(103): octal literals 0100 are
deprecated, use std.conv.octal!100 instead
druntime/src/core/sys/posix/sys/stat.d(142): octal literals 0400 are
deprecated, use std.conv.octal!400 instead

I was also disturbed to notice that the druntime modules are ALL built
with the -d flag, so this isn't showing up when building druntime.
But I don't understand why this error isn't showing up in the
autotester, when building d_do_test.