libusb: fix clock_gettime librt dependency check

libusb: fix clock_gettime librt dependency check

The detection of the librt dependency of clock_gettime in glibc before
2.17 is broken. We do not support glibc older than 2.17 for target, but
we still need to support hosts using old glibc. Add a patch fixing that.

Should fix (host-imx-usb-loader):
http://autobuild.buildroot.net/results/0a1/0a156449e5f38a6092ab9c88e3e3f5ea9abc0f03/
http://autobuild.buildroot.net/results/347/347f1b9bce2f0854e8ca6d49b9a9b3fa55de24b1/
http://autobuild.buildroot.net/results/f6a/f6a3a62909ccb500ca122ec3f03119d7706fb88a/

Cc: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>