linux: use CLOCK_MONOTONIC_RAW as this is not subject to NTP
VDPAU: improve error handling
[build] enable gtest configure by default.
Merge pull request #4635 from FernetMenta/linux

linux: use CLOCK_MONOTONIC_RAW as this is not subject to NTP
Merge pull request #4638 from FernetMenta/vdpau2

VDPAU: improve error handling (ffmpeg 2.2)
Merge pull request #4640 from jmarshallnz/gtest_on

[build] enable gtest configure by default.
Merge remote-tracking branch 'upstream/master'