pgsql: Disable excessive FP optimization by recent versions of gcc.

Disable excessive FP optimization by recent versions of gcc.

Suggested solution from Tom Lane. Problem discovered, probably not
for the first time, while testing the mingw-w64 32 bit compiler.

Backpatched to all live branches.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/5878a328e36b7f59c6c173212b77d0536e8804dd

Modified Files
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configure    |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
configure.in |    2 +
2 files changed, 63 insertions(+), 0 deletions(-)