testsuite: Exclude end-of-line characters from get_valueof result

testsuite: Exclude end-of-line characters from get_valueof result

The get_valueof procedure allows tests to conveniently make gdb evaluate
an expression an return the value as a string.  However, it includes an
end-of-line character in its result.  I stumbled on this when trying to
use that result as part of a regex further in a test.

You can see this for example by adding a puts in
gdb.dwarf2/implref-struct.exp:get_members:

    set members [get_valueof "" ${var} ""]
    puts "<$members>"

The output is

    <{a = 0, b = 1, c = 2}
    >

This is because the regex in get_valueof is too greedy, the captured
portion matches anything up to the gdb_prompt, including the end of line
characters.  This patch changes it to capture everything but end of line
characters.

The output of the puts becomes:

    <{a = 0, b = 1, c = 2}>

I tested this by running gdb.dwarf2/implref-array.exp and
gdb.dwarf2/implref-struct.exp, the two only current users of that
procedure.

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (get_valueof): Don't capture end-of-line
	characters.