meson: tweak hardening options for Windows

meson: tweak hardening options for Windows

meson.build has been enabling ASLR _only_ for debug builds since
commit d2147e04f95f ("configure: move Windows flags detection to meson",
2022-05-07); instead it was supposed to disable it for debug builds.

However, the flag has been enabled for DLLs upstream for roughly 2
years (https://sourceware.org/bugzilla/show_bug.cgi?id=19011), and
also by some distros including Debian for 6 years even
(https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=836365).

Enable it unconditionally; we can fix the reversed logic of commit
d2147e04f95f later if there are any reports, but for now just
enable the hardening.

Also add -Wl,--high-entropy-va, which also controls ASLR.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>