pgsql: Move pg_upgrade's Windows link() implementation to AC_REPLACE_FU

Move pg_upgrade's Windows link() implementation to AC_REPLACE_FUNCS

This way we can make use of it in other components as well, and it
fits better with the rest of the build system.

Discussion: https://www.postgresql.org/message-id/flat/72fff73f-dc9c-4ef4-83e8-d2e60c98df48%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0ad6f848eef267489d4aee7306c16f96454b7a64

Modified Files
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configure                       | 13 +++++++++++++
configure.in                    |  1 +
src/bin/pg_upgrade/file.c       | 27 ++-------------------------
src/bin/pg_upgrade/pg_upgrade.h |  2 --
src/include/pg_config.h.in      |  3 +++
src/include/port.h              |  4 ++++
src/port/link.c                 | 35 +++++++++++++++++++++++++++++++++++
src/tools/msvc/Mkvcbuild.pm     |  2 +-
src/tools/msvc/Solution.pm      |  1 +
9 files changed, 60 insertions(+), 28 deletions(-)