Fix global variable collision in gdb.multi/multi-kill.exp

The new gdb.multi/multi-kill.exp testcase added an 'testpid' array,
which may conflict with other global 'testpid' variables used by other
testcases, resulting in:

 ...
 ERROR: tcl error sourcing
 /data/gdb_versions/devel/src/gdb/testsuite/gdb.multi/multi-kill.exp.
 ERROR: can't set "testpid(1)": variable isn't array
     while executing
 "set testpid($num) [get_integer_valueof "pid" -1]"

or

 $ runtest gdb.threads/check-libthread-db.exp gdb.multi/multi-kill.exp
 ...
 Running /home/pedro/gdb/binutils-gdb/src/gdb/testsuite/gdb.multi/multi-kill.exp ...
 Running /home/pedro/gdb/binutils-gdb/src/gdb/testsuite/gdb.threads/check-libthread-db.exp ...
 ERROR: tcl error sourcing /home/pedro/gdb/binutils-gdb/src/gdb/testsuite/gdb.threads/check-libthread-db.exp.
 ERROR: can't set "testpid": variable is array
     while executing
 "set testpid [spawn_id_get_pid $test_spawn_id]"
     ("uplevel" body line 8)

Fix this with a namespace, like gdb.linespec/explicit.exp does.

gdb/testsuite/ChangeLog:
2020-05-15  Pedro Alves  <palves@redhat.com>

	* gdb.multi/multi-kill.exp: Wrap in namespace.
	(start_inferior): Add TESTPID parameter.  Use it instead of the
	testpid global.
	(top level): Define empty TESTPID array, and pass it down to
	start_inferior.

2 files changed, 22 insertions, 5 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 6c02583..93ad65b3 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2020-05-15  Pedro Alves  <palves@redhat.com>
+
+	* gdb.multi/multi-kill.exp: Wrap in namespace.
+	(start_inferior): Add TESTPID parameter.  Use it instead of the
+	testpid global.
+	(top level): Define empty TESTPID array, and pass it down to
+	start_inferior.
+
 2020-05-14  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.fortran/nested-funcs-2.exp: Use gdb_test_stdio to test inferior
diff --git a/gdb/testsuite/gdb.multi/multi-kill.exp b/gdb/testsuite/gdb.multi/multi-kill.exp
index ce60750..03bf844 100644
--- a/gdb/testsuite/gdb.multi/multi-kill.exp
+++ b/gdb/testsuite/gdb.multi/multi-kill.exp
@@ -39,11 +39,15 @@ save_vars { GDBFLAGS } {
     clean_restart ${binfile}
 }
 
+# Wrap the entire test in a namespace to avoid contaminating other tests.
+namespace eval $testfile {
+
 # Start inferior NUM and record its PID in the TESTPID array.
 
-proc start_inferior {num} {
+proc start_inferior {num testpid} {
     with_test_prefix "start_inferior $num" {
-	global testpid binfile srcfile
+	upvar $testpid tpid
+	global binfile srcfile
 
 	if {$num != 1} {
 	    gdb_test "add-inferior" "Added inferior .*" \
@@ -58,8 +62,8 @@ proc start_inferior {num} {
 	gdb_run_cmd
 	gdb_test "" ".*reakpoint .*, initialized .*${srcfile}.*" "run"
 
-	set testpid($num) [get_integer_valueof "pid" -1]
-	if {$testpid($num) == -1} {
+	set tpid($num) [get_integer_valueof "pid" -1]
+	if {$tpid($num) == -1} {
 	    return -1
 	}
 
@@ -71,8 +75,11 @@ proc start_inferior {num} {
 # is killed while we're handling a killed event.
 set NUM_INFS 10
 
+# The array holding each inferior's PID, indexed by inferior number.
+array set testpid {}
+
 for {set i 1} {$i <= $NUM_INFS} {incr i} {
-    if {[start_inferior $i] < 0} {
+    if {[start_inferior $i testpid] < 0} {
 	return -1
     }
 }
@@ -125,3 +132,5 @@ for {set i 2} {$i <= $NUM_INFS} {incr i} {
 	    "continue to SIGKILL"
     }
 }
+
+}