pgsql: Add gitignore for mingw/cygwin build outputs

Add gitignore for mingw/cygwin build outputs

Noted by Radosław Smogura

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/1710752a50a37c965c964e362635d9ba3a333dcf

Modified Files
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.gitignore | 2 ++
src/backend/.gitignore | 1 +
2 files changed, 3 insertions(+), 0 deletions(-)