configure: Add -Werror to PIE probe

Without -Werror, the probe may succeed, but then compilation fails
later when -Werror is added for other reasons.  Shows up on windows,
where the compiler complains about -fPIC.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200401214756.6559-1-richard.henderson@linaro.org>
Message-Id: <20200403191150.863-13-alex.bennee@linaro.org>