[gdb/testsuite] Fix gdb.dwarf2/dw2-using-debug-str.exp with cc-with-dwz-m

When running with target board cc-with-dwz-m, we run into:
...
(gdb) file dw2-using-debug-str-no-debug-str^M
Reading symbols from dw2-using-debug-str-no-debug-str...^M
(gdb) FAIL: gdb.dwarf2/dw2-using-debug-str.exp: file dw2-using-debug-str
...

With native, the .debug_str section is present in the
dw2-using-debug-str executable, and removed from the
dw2-using-debug-str-no-debug-str executable.  When loading the latter, a dwarf
error is triggered.

With cc-with-dwz-m, the .debug_str section is not present in the
dw2-using-debug-str executable, because it's already moved to
.tmp/dw2-using-debug-str.dwz.  Consequently, the removal has no effect, and no
dwarf error is triggered, which causes the FAIL.

The same problem arises with target board cc-with-gnu-debuglink.

Fix this by detecting whether the .debug_str section is missing, and skipping
the remainder of the test-case.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-08-02  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/dw2-using-debug-str.exp: Handle missing .debug_str
	section in dw2-using-debug-str.

1 files changed, 13 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-using-debug-str.exp b/gdb/testsuite/gdb.dwarf2/dw2-using-debug-str.exp
index 09f58d3..e274d0c 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-using-debug-str.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-using-debug-str.exp
@@ -100,6 +100,19 @@ if ![runto_main] {
 # field names, all of which are stored in the .debug_str section.
 gdb_test "p global_var" " = \\{aa = 0, bb = 0, cc = 0\\}"
 
+# Verify that the executable actually contains a .debug_str section, before
+# trying to remove it.  This can be missing with target boards
+# cc-with-dwz-m.exp and cc-with-gnu-debuglink.exp.  Handle this by
+# skipping the remainder of the test-case.
+set debug_str_section "${binfile}-debug-str"
+set args "--dump-section .debug_str=debug_str_section $binfile"
+set result [remote_exec host "[gdb_find_objcopy] $args"]
+set status [lindex $result 0]
+set output [lindex $result 1]
+if { $status == 0 && ![string equal $output ""] } {
+    return -1
+}
+
 # Now copy the executable, and remove the .debug_str section.  This
 # creates an executable with an invalid DWARF configuration.  GDB
 # should give an error when trying to read the debug information from