apt: add -fno-strict-aliasing to CXXFLAGS to fix SHA256 bug

apt: add -fno-strict-aliasing to CXXFLAGS to fix SHA256 bug

Recently we've begun seeing issues with apt SHA256 generation/checking on some
distros (fedora 35, alma 8). The version of apt in dunfell uses its own
SHA256 code, not a standard library.

Investigation reveals that the issue is related to -fstrict-aliasing enabled by
-O2 optimization, so turn it off with -fno-strict-aliasing

Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>