[gdb/testsuite] Require local host in gdb.base/bg-exec-sigint-bp-cond.exp

I noticed that gdb.base/bg-exec-sigint-bp-cond.exp fails for remote host
(concretely, host board local-remote-host and target board
remote-gdbserver-on-localhost):
...
(gdb) c&^M
Continuing.^M
(gdb) bash: line 0: kill: (23834) - Operation not permitted^M
^M
Breakpoint 2, foo () at bg-exec-sigint-bp-cond.c:23^M
23        return 0;^M
...
due to getting gdb's pid like this:
...
    set gdb_pid [exp_pid -i [board_info host fileid]]
...

For remote host using ssh, this returns the pid of the ssh session on build.

Fix this by requiring local host.

Tested on x86_64-linux.

gdb/testsuite/gdb.base/bg-exec-sigint-bp-cond.exp

@@ -16,6 +16,10 @@
 # Check that sending GDB a SIGINT while handling execution control
 # does not interrupt the execution control.
 
+# The way we get the pid of gdb doesn't work with remote host.  We get the
+# pid of the ssh session on build instead.
+require {!is_remote host}
+
 standard_testfile
 
 if {[build_executable "failed to prepare" $testfile $srcfile debug]} {