weston: add build fix for clock_gettime() in librt
Over time weston has been manually adding -lrt LDADDs to the Makefile
for clock_gettime() using sources. However this isn't 100% correct since
"modern" glibc versions don't require it so switch all over to a
configure test for that purpose. Fixes:
http://autobuild.buildroot.net/results/a16/
a165f439cf5a81c79fe3fa3af7a2a5a30022e7ed/
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
[Thomas: fixed autobuilder reference.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>