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
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/24b96804d588da262ae0d3958e14638de217445a

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