Hi,

This patch fixes the type-punning warnings that the GCC 4.1 branch
issues when compiling the GDB code base.

The fixes for the .y files are safe, since the casts only perform a
non-identity conversion when code paths that are never taken.  The two
other cases are situations in which the use of opaque types forces us
to violate the ISO C string aliasing rules; the one in tui/tui-data.c
is safe in that we never access the affected data structures with the
wrong type.  In varobj.c that's much trickier to prove, but since it's
in a separate translation unit from the call, what we have now is no
safer than what we get after my patch.

Build-tested on amd64-linux-gnu.  Ok to install?