default is to enable sim if there's support for the cpu).
The current list of "known to work" contains arches with G_SIM_OBS
already set: powerpc, powerpc64 and mips.
There's arm support in sim, but committed configs for arm do not have
G_SIM_OBS set, so I'm not enabling it here.
There's SH support in sim, but it fails to build out of the box, and
since we didn't build SH sim support for gdb 5.3, we keep it disabled.
Other arches shouldn't be affected, as there's no support for them in sim.
top-level configure, but to ${MAKE} configure-host as well.
Add more vars (for readline mostly) so that there's no configure
warnings about tests skipped b/c of cross-compilation.
gdb comes with its own copy of GNU readline 5.x, but
-I${DESTDIR}/usr/include stuffed at the beginning of the command line
makes it find our compat readline/readline.h (emulating readline 2.x)
that conflicts with the readline 5.x includes.
Makes README.mknative instructions actually work instead of failing
midway b/c of conflicting tilde_expand() prototypes.
