Remove uses of "eval" from gdb testsuite

This patch removes a lot of uses of the Tcl "eval" proc from the gdb
test suite.  In most cases the {*} "splat" expansion is used instead.

A few uses of eval remain, primarily ones that were more complicated
to untangle.

In a couple of tests I also replaced some ad hoc code with
string_to_regexp.

Tested on x86-64 Fedora 40.

Reviewed-By: Tom de Vries <tdevries@suse.de>