pgsql: Windows: use GetSystemTimePreciseAsFileTime if available

Windows: use GetSystemTimePreciseAsFileTime if available

PostgreSQL on Windows 8 or Windows Server 2012 will now
get high-resolution timestamps by dynamically loading the
GetSystemTimePreciseAsFileTime function. It'll fall back to
to GetSystemTimeAsFileTime if the higher precision variant
isn't found, so the same binaries without problems on older
Windows releases.

No attempt is made to detect the Windows version. Only the
presence or absence of the desired function is considered.

Craig Ringer

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8001fe67a3d66c95861ce1f7075ef03953670d13

Modified Files
--------------
src/backend/main/main.c | 6 ++++++
src/include/port.h | 2 ++
src/port/gettimeofday.c | 53 +++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 59 insertions(+), 2 deletions(-)