[Ada] Update signal constants for GNU/Linux

[Ada] Update signal constants for GNU/Linux

Add the signal SIGSYS and mark the glibc reserved real-time signals
(32-34) as reserved rather than not maskable.

2018-11-14  Patrick Bernardi  <bernardi@adacore.com>

gcc/ada/

	* libgnarl/a-intnam__linux.ads: Add SIGSYS.
	* libgnarl/s-linux__alpha.ads, libgnarl/s-linux__android.ads,
	libgnarl/s-linux__hppa.ads, libgnarl/s-linux__mips.ads,
	libgnarl/s-linux__riscv.ads, libgnarl/s-linux__sparc.ads,
	libgnarl/s-linux__x32.ads: Rename SIGLTHRRES, SIGLTHRCAN and
	SIGLTHRDBG to SIG32, SIG33 and SIG34 as their names are
	implementation specific.
	* libgnarl/s-osinte__linux.ads, libgnarl/s-linux.ads: Add
	SIGSYS.  Move SIG32, SIG33 and SIG34 from the unmasked list to
	the reserved list.

gcc/testsuite/

	* gnat.dg/rt_signals.adb: New testcase.

From-SVN: r266136