[PATCH] gdb: Unset PROMPT_COMMAND before testing

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

One of the GDB tests starts up a sub-shell and runs a few commands in
it.  In some cases, a users PROMPT_COMMAND might not work in the
sub-shell GDB starts, which could cause the shell to emit unexpected
warnings or errors, this in turn could cause tests to fail.

The current example is gdb.base/batch-preserve-term-settings.exp, but
there could be others in the future.

I don't see any regressions with this patch, but I do now see 5
additional passes on gdb.base/batch-preserve-term-settings.exp.

OK to apply?

Thanks,
Andrew

---

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (gdb_init): Unset PROMPT_COMMAND.
---
 gdb/testsuite/ChangeLog   | 4 ++++
 gdb/testsuite/lib/gdb.exp | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index a74f97465e..053bc65e09 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -4626,6 +4626,11 @@ proc gdb_init { test_file_name } {
     # especially having color output turned on can cause tests to fail.
     setenv GREP_OPTIONS ""
 
+    # Some tests run a shell.  If a user has PROMPT_COMMAND set then
+    # there's no guarantee that what it's set to will work correctly
+    # within the sub-shells we run.  For safety clear it.
+    setenv PROMPT_COMMAND ""
+
     # Clear $gdbserver_reconnect_p.
     global gdbserver_reconnect_p
     set gdbserver_reconnect_p 1
-- 
2.12.2