some minor s390-specific syscall-related updates

This is the second version of "[man-pages PATCH 0/5] some minor s390 syscall updates" patch set, Message-ID <[email protected]>.

Changes since v1:
* Changes proposed by Heiko Carstens were incorporated.
* The patch proposed by Heiko Carstens regarding signum behaviour change was incorporated; however, I've tweaked it a bit, as in the end I decided that it worth noting the original semantics of signum argument, since the default handler for real-time signals terminates application.
* Minor rewording here and there.
* "s390_sthyi.2: wfix" patch was dropped as the change has been already applied in commit 2cd9bbfa48 "Removed trailing white space at end of lines".

Eugene Syromyatnikov (3):
s390_runtime_instr.2: add a note about runtime_instr.h availability s390_sthyi.2: some minor additions
man2: describe s390_guarded_storage s390-specific system call

Heiko Carstens (1):
s390_runtime_instr.2: document signum argument behavior change

 man2/s390_guarded_storage.2 | 150 ++++++++++++++++++++++++++++++++++++++++++++
 man2/s390_runtime_instr.2   |  28 +++++++--
 man2/s390_sthyi.2           |  11 ++++
 3 files changed, 185 insertions(+), 4 deletions(-)
 create mode 100644 man2/s390_guarded_storage.2

2.1.4