pgsql: Teach MSVC build system about building foreign data wrappers.

Log Message:
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Teach MSVC build system about building foreign data wrappers.

Should fix recent buildfarm breakage.

Modified Files:
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pgsql/src/tools/msvc:
Mkvcbuild.pm (r1.34 -> r1.35)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Mkvcbuild.pm?r1=1.34&r2=1.35)