Ada: Fix too late initialization of tasking runtime with standalone library

Ada: Fix too late initialization of tasking runtime with standalone library

The Tasking_Runtime_Initialize routine installs the tasking version of the
RTS_Lock manipulation routines and thus needs to be called very early before
the elaboration of all the Ada units of the program, including those of the
runtime itself.

This is guaranteed by the binder when the tasking runtime is explicitly
dragged into the link.  However, for a standalone dynamic library that
does not depend on the tasking runtime and is auto-initialized, no such
guarantee holds, even though the library might be later dragged into a
link that contains the tasking runtime.

This change causes the routine to be called even earlier, in particular
at load time when a (standalone) dynamic library is involved in the link,
so as to meet the requirements.  It will cause the routine to be called
twice if the main subprogram is generated by the binder, but this is
harmless since the routine is idempotent.

ada/
	* libgnarl/s-tasini.adb (Tasking_Runtime_Initialize): Add pragma
	Linker_Constructor for the procedure.