pgsql: Use the preferred version of xsubpp, not necessarily the one tha

Use the preferred version of xsubpp, not necessarily the one that came with the
distro version of perl.

David Wheeler and Alex Hunsaker.

Backpatch to 9.1 where it applies cleanly. A simple workaround is available for earlier
branches, and further effort doesn't seem warranted.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ba00ab0b111a0cbbac612e8ea8b0d5f96534102e

Modified Files
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src/pl/plperl/GNUmakefile | 7 +++++--
src/tools/msvc/Mkvcbuild.pm | 5 ++++-
2 files changed, 9 insertions(+), 3 deletions(-)