[gdb/testsuite] Add cond_wrap proc
Add a new proc cond_wrap, that can be used to replace the repetitive:
...
if { $cond } {
wrap {
<body>
}
} else {
<body>
}
...
with the shorter:
...
cond_wrap $cond wrap {
<body>
}
...
Tested on x86_64-linux.