Callgrind: Broader handling of _dl_runtime_resolve variants

This is a supplement to commit 86277041

To improve its results, Callgrind does special handling for
the runtime linker entry point to resolve symbols. However,
it only used the exact symbol name "_dl_runtime_resolve",
as well as specific machine code templates (when the runtime
linker was stripped from symbol names) as basis.
Recent glibc added multiple similar symbol names as variants,
such as _dl_runtime_resolve_xsave.

The above-mentioned commit 86277041 solves this by extending
the check for machine code templates for specific Linux
distributions.
This patch extends this for more architectures and variants
by checking if a function starts with "_dl_runtime_resolve".
Furthermore, the original function names of the variants
still are visible in the output (and not forced to the prefix).

While the heuristic that every function symbol starting
with the prefix "_dl_runtime_resolve" as being an entry point
into the runtime linker for resolving a function address may
be a bit rough, this prefix is not expected to be used often in
other source code for anything else.

The worst case is a slightly misleading call graph only
visible in a very specific situation: if the wrongly-detected
function does a tail call (ie instead of returning, jumping
to another function), it will be shown as 2 calls in a row
from the original caller.

callgrind/fn.c

@@ -665,7 +665,7 @@ fn_node* CLG_(get_fn_node)(BB* bb)
       if (bb->sect_kind == Vg_SectPLT)	
 	fn->skip = CLG_(clo).skip_plt;
 
-      if (VG_(strcmp)(fn->name, "_dl_runtime_resolve")==0) {
+      if (VG_(strncmp)(fn->name, "_dl_runtime_resolve", 19)==0) {
 	  fn->pop_on_jump = True;
 
 	  if (VG_(clo_verbosity) > 1)