Improve modify_ldt, [gs]et_thread_area docs

The docs for set_thread_area, get_thread_area, and modify_ldt are pretty bad, and there have been a number of kernel changes lately. Improve and update the docs.

Andy Lutomirski (2):
modify_ldt.2: Overhaul the documentation arch_prctl.2, set_thread_area.2, get_thread_area.2: Improve TLS
documentation

 man2/arch_prctl.2      |  22 +++++++----
 man2/get_thread_area.2 |  58 +---------------------------
 man2/modify_ldt.2      | 101 ++++++++++++++++++++++++++++++++++++++-----------
 man2/set_thread_area.2 |  93 ++++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 180 insertions(+), 94 deletions(-)

2.1.0