gdbserver short-circuit-argument-list failures

This patch fixes test case failures observed when running
short-circuit-argument-list.exp with gdb server boards. Thanks to Sergio
Durigan Junior for pointing this out.

Assertions failed with the native{,-extended}-gdbserver boards as the
standard output from the test program appears in a different location
than observed on non-gdbserver boards. This standard output was used to
determine whether a function, which had been logically short-circuited,
was called or not. Since the location of the standard out cannot be
relied upon to verify this, a new mechanism was needed.

The test program now records function calls in variables named the same
as the function with a "_called" suffix. These variables can then be
queried from the test case to verify the occurrence of a call.

A method to reset the call counts has been included in the test case, so
that any future assertions added to this test can ensure a fresh set of
initial values before proceeding. Not resetting values between groups of
assertions creates a dependency between them, which increases the
likelihood that a single failure causes subsequent assertions to fail.

Regression tested on x86_64, aarch64 and ppc64le.
Regression tested with Ada on x86_64.
Regression tested with the native{,-extended}-gdbserver boards on x86_64.