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_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/6f630af876b5525d222c5b8589f6d973475801ea

Modified Files
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configure | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
configure.in | 2 ++
2 files changed, 56 insertions(+), 0 deletions(-)