[perl #38840] Use File::Spec instead of /dev/null

[Will Coleda]

# New Ticket Created by Will Coleda
# Please include the string: [perl #38840]
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# <URL: https://rt.perl.org/rt3/Ticket/Display.html?id=38840 >

The following files reference '/dev/null/' directly, and should be
updated to use the File::Spec's interface instead of either rolling
their own or assuming '/dev/null' works everywhere.

languages/punie/t/base_term.t
lib/Parrot/Configure/Step.pm
lib/Parrot/Test/Perl6.pm
lib/Parrot/Test.pm
t/configure/step.t
t/examples/library.t
t/library/pcre.t
t/run/exit.t
t/run/options.t
tools/dev/lib_deps.pl