[clang] [test] Improve XFAIL patterns for aarch64 msvc (#153397)
Unless relevant (which it very seldom is), avoid checking specifically
for the "pc" vendor field; mingw environments often use "w64" as vendor
- but not always.
In this case, this test has been passing in mingw configurations lately;
the previous XFAIL pattern would cause the test to unexpectedly succeed
if running with a triple with a "pc" vendor field.
Instead reinstate the checking for an -msvc environment here; this
essentially reverts 8e029d9e35092d1440dafc8991e73fb8c3b323d7 (and the
related typo fix 301f3da5162499965287338a0cd52309fb28e8b8).
I'm not sure how 8e029d9e35092d1440dafc8991e73fb8c3b323d7 concluded that
this issue affected the gnu ABI (mingw) as well; I rechecked building
that commit, and at that point, this test did pass for an aarch64 mingw
target. (Due to the -pc- triple, the false positive XFAIL match hasn't
been noticed before.)