Ensure HOMEBREW_ARCHFLAGS is always a string
Move -m32 and -m64 filtering up one level

These flags cannot be used behind -Xarch_<arch>, so stop filtering them
there.
wine --devel 1.7.18

Closes #29119.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Fix duplicate -stdlib flags in cxxld mode

When the cc wrapper is in cxxld mode, -stdlib= is added by both cxxflags
and ldflags, but they are never used separately, so this results in
duplicate flags.