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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REL8_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/01e80a0c2862290bf417f699c414578c91702ef0

Modified Files
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configure | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
configure.in | 2 ++
2 files changed, 52 insertions(+), 0 deletions(-)