[committed][gdb/testsuite] Add missing initial prompt read in multidictionary.exp

[Tom de Vries <tdevries at suse dot de>]

Hi,

When running multidictionary.exp in conjunction with:
...
$ stress -c $(($(cat /proc/cpuinfo | grep -c "^processor") + 1))
...
we get:
...
Running gdb/testsuite/gdb.dwarf2/multidictionary.exp ...
ERROR: Couldn't load multidictionary into gdb.

                === gdb Summary ===

nr of unresolved testcases       1
...

The multidictionary test-case needs -readnow, and achieves this using:
...
gdb_spawn_with_cmdline_opts "-readnow"
gdb_load
...
but the initial gdb prompt is not read.  Usually, the following gdb_load
command accidentally consumes that initial prompt (at the gdb_expect for the
kill command in gdb_file_cmd).  But under high load, that doesn't happen and
we run into the error.

Fix this by consuming the initial gdb prompt after spawning gdb.

Tested on x86_64-linux.

Committed to trunk.

Thanks,
- Tom

[gdb/testsuite] Add missing initial prompt read in multidictionary.exp

gdb/testsuite/ChangeLog:

2019-07-23  Tom de Vries  <tdevries@suse.de>

	PR testsuite/24842
	* gdb.dwarf2/multidictionary.exp: Consume initial prompt after
	gdb_spawn_with_cmdline_opts.

---
 gdb/testsuite/gdb.dwarf2/multidictionary.exp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gdb/testsuite/gdb.dwarf2/multidictionary.exp b/gdb/testsuite/gdb.dwarf2/multidictionary.exp
index 5588ef2144..c307ed8adc 100644
--- a/gdb/testsuite/gdb.dwarf2/multidictionary.exp
+++ b/gdb/testsuite/gdb.dwarf2/multidictionary.exp
@@ -148,6 +148,12 @@ if {[build_executable $testfile.exp $testfile [list $asm_file $srcfile] {}] \
 
 # We force the DIEs above to be read in via "-readnow".
 gdb_spawn_with_cmdline_opts "-readnow"
+set test "initial prompt"
+gdb_test_multiple "" $test {
+    -re ".*$gdb_prompt $" {
+	pass "$test"
+    }
+}
 gdb_load $binfile
 
 # All we need to do is check whether GDB is alive.  Without