[pushed] [gdb/testsuite] Fix gdb.dwarf2/dw-form-strx-out-of-bounds.exp

With test-case gdb.dwarf2/dw-form-strx-out-of-bounds.exp, I usually get:
...
(gdb) file dw-form-strx-out-of-bounds
Reading symbols from dw-form-strx-out-of-bounds...
(gdb) ptype global_var
DWARF Error: Offset from DW_FORM_GNU_str_index or DW_FORM_strx pointing \
  outside of .debug_str_offsets section in CU at offset 0x2d1 [in module \
  dw-form-strx-out-of-bounds]
No symbol "global_var" in current context.
(gdb) PASS: $exp: ptype global_var
...

But I just ran into:
...
(gdb) file dw-form-strx-out-of-bounds^M
Reading symbols from dw-form-strx-out-of-bounds...
DWARF Error: Offset from DW_FORM_GNU_str_index or DW_FORM_strx pointing \
  outside of .debug_str_offsets section in CU at offset 0x2df [in module \
  dw-form-strx-out-of-bounds]^M
(gdb) ptype global_var^M
No symbol "global_var" in current context.^M
(gdb) FAIL: $exp: ptype global_var
...

Fix this by:
- using "maint set dwarf synchronous on" to ensure that the error happens
  during the file command
- updating the matching to check $gdb_file_cmd_msg

Tested gdb.dwarf2/dw-form-strx-out-of-bounds.exp and gdb.dwarf2/dw-form-strx.exp
using make-check-all.sh on x86_64-linux.
---
 gdb/testsuite/gdb.dwarf2/dw-form-strx-out-of-bounds.exp | 7 +++----
 gdb/testsuite/gdb.dwarf2/dw-form-strx.exp.tcl           | 8 +++++++-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/dw-form-strx-out-of-bounds.exp b/gdb/testsuite/gdb.dwarf2/dw-form-strx-out-of-bounds.exp
index be7323bce95..e1e28eb432f 100644
--- a/gdb/testsuite/gdb.dwarf2/dw-form-strx-out-of-bounds.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw-form-strx-out-of-bounds.exp
@@ -34,8 +34,7 @@ set re_dwarf_error \
 set re_in_module \
     {in module [^\r\n]+}
 set re_in_module [string_to_regexp {[}]$re_in_module[string_to_regexp {]}]
+gdb_assert {[regexp "$re_dwarf_error $re_in_module" $gdb_file_cmd_msg]}
+
 set re_no_symbol [string_to_regexp {No symbol "global_var" in current context.}]
-gdb_test "ptype global_var" \
-    [multi_line \
-	 "$re_dwarf_error $re_in_module"\
-	 $re_no_symbol]
+gdb_test "ptype global_var" $re_no_symbol
diff --git a/gdb/testsuite/gdb.dwarf2/dw-form-strx.exp.tcl b/gdb/testsuite/gdb.dwarf2/dw-form-strx.exp.tcl
index 931c935ccae..b261dc654af 100644
--- a/gdb/testsuite/gdb.dwarf2/dw-form-strx.exp.tcl
+++ b/gdb/testsuite/gdb.dwarf2/dw-form-strx.exp.tcl
@@ -54,11 +54,17 @@ Dwarf::assemble $asm_file {
     }
 }
 
-if { [prepare_for_testing "failed to prepare" ${testfile} \
+if { [build_executable "failed to prepare" ${testfile} \
 	  [list $srcfile $asm_file] {nodebug}] } {
     return
 }
 
+clean_restart
+
+gdb_test_no_output "maint set dwarf synchronous on"
+
+gdb_load $binfile
+
 # Let includers know prepare_for_testing was done, without having to check
 # source return status.
 set prepare_for_testing_done 1

base-commit: 8b3ea407f65571000c9fc3d79081b65d1b4e3759
-- 
2.51.0