[gdb/exp] Fix exception when printing optimized out vla

When compiling vla-optimized-out.c with -O3 and a recent gcc, and trying to
print the vla a in f1, we run into this gdb exception:
...
Cannot find matching parameter at DW_TAG_call_site 0x4003be at main
...

This is a regression introduced by 42dc7699a2 "[gdb/exp] Fix printing of type
of optimized out vla".

This patch fixes the regression by wrapping the ctx.eval call in
dwarf2_locexpr_baton_eval in try/catch, similar to what is done in
dwarf2_evaluate_loc_desc_full.

Build and reg-tested on x86_64-linux.

2018-07-25  Tom de Vries  <tdevries@suse.de>

	* dwarf2loc.c (dwarf2_locexpr_baton_eval): Wrap ctx.eval call in
	try/catch.

	* gdb.base/vla-optimized-out-o3.exp: New file.  Reuse
	vla-optimized-out.c.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2018-07-25  Tom de Vries  <tdevries@suse.de>
+
+	* dwarf2loc.c (dwarf2_locexpr_baton_eval): Wrap ctx.eval call in
+	try/catch.
+
 2018-07-25  Jan Vrany  <jan.vrany@fit.cvut.cz>
 
 	* breakpoint.c (enable_disable_bp_num_loc): Notify observers.

gdb/dwarf2loc.c

@@ -2573,7 +2573,26 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
   ctx.ref_addr_size = dwarf2_per_cu_ref_addr_size (dlbaton->per_cu);
   ctx.offset = dwarf2_per_cu_text_offset (dlbaton->per_cu);
 
-  ctx.eval (dlbaton->data, dlbaton->size);
+  TRY
+    {
+      ctx.eval (dlbaton->data, dlbaton->size);
+    }
+  CATCH (ex, RETURN_MASK_ERROR)
+    {
+      if (ex.error == NOT_AVAILABLE_ERROR)
+	{
+	  return 0;
+	}
+      else if (ex.error == NO_ENTRY_VALUE_ERROR)
+	{
+	  if (entry_values_debug)
+	    exception_print (gdb_stdout, ex);
+	  return 0;
+	}
+      else
+	throw_exception (ex);
+    }
+  END_CATCH
 
   switch (ctx.location)
     {

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2018-07-25  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.base/vla-optimized-out-o3.exp: New file.  Reuse
+	vla-optimized-out.c.
+
 2018-07-25  Jan Vrany  <jan.vrany@fit.cvut.cz>
 
 	* gdb.mi/mi-breakpoint-location-ena-dis.cc: New file.

gdb/testsuite/gdb.base/vla-optimized-out-o3.exp

@@ -0,0 +1,36 @@
+# Copyright 2018 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check whether we can print an optimized-out vla.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile "vla-optimized-out.c" \
+	  {debug optimize=-O3}] } {
+    return -1
+}
+
+proc vla_optimized_out { } {
+    if ![runto f1] {
+	fail "can't run to f1"
+	return
+    }
+
+    gdb_test "p a" \
+	{ = <optimized out>} \
+	"printed optimized out vla"
+}
+
+vla_optimized_out