Clarify the #error about glibc-sched.h requirin...
Clarify the #error about glibc-sched.h requirin...

Clarify the #error about glibc-sched.h requiring sched.h with _GNU_SOURCE defined

This commit was SVN r3178.

shekkbuilder/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc