utils: Work around mingw strto*l bug with 0x

Mingw recognizes that "0x" has value 0 without setting errno, but
fails to advance endptr to the trailing garbage 'x'.  This in turn
showed up in our recent testsuite additions for qemu_strtosz (commit
1657ba44 utils: Enhance testsuite for do_strtosz()); adjust our
remaining tests to show that we now work around this windows bug.

This patch intentionally fails check-syntax for use of strtol.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210317143325.2165821-3-eblake@redhat.com>
Message-Id: <20210323165308.15244-15-alex.bennee@linaro.org>