pgsql: Suppress compiler warnings in ecpg test on newer Windows toolcha

Suppress compiler warnings in ecpg test on newer Windows toolchains.

nan_test.pgc supposed that it could unconditionally #define isnan()
and isinf() on WIN32. This was evidently copied at some point from
src/include/port/win32.h, but nowadays there's a test on _MSC_VER
there. Make nan_test.pgc look the same.

Per buildfarm warnings. There's no evidence this produces anything
worse than a warning, and besides it's only a test case, so I don't
feel a need to back-patch.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/c5658a0764d5ac5ea8c2c11d27c62d5472234227

Modified Files
--------------
.../ecpg/test/expected/pgtypeslib-nan_test.c | 102 +++---
.../ecpg/test/expected/pgtypeslib-nan_test.stderr | 354 ++++++++++-----------
src/interfaces/ecpg/test/pgtypeslib/nan_test.pgc | 2 +
3 files changed, 231 insertions(+), 227 deletions(-)