sim: use -Werror when probing for supported warning flags

sim: use -Werror when probing for supported warning flags

When building with clang, we get:

    error: unknown warning option '-Wmissing-parameter-type' [-Werror,-Wunknown-warning-option]

This is because clang only warns by default when encountering an unknown
warning option, and the probe for supported warning flags is done
without -Werror.  All flags are therefore accepted by configure, but
then it breaks when actually compiling a source file with -Werror.

This is equivalent to this commit in gdb:

    3e019bdc20eb81b91ab5bc774386201b874c0bac
    gdb: Use -Werror when checking for (un)supported warning flags

We then see some other compilation errors when building with clang and
-Werror, they can be dealt with later.