ci: disable __thread support for Windows msys2 build

ci: disable __thread support for Windows msys2 build

Our Windows msys2 build is now broken after AppVeyor's recent image
update from clang/lld 15.0.7-3 to 16.0.0-1.

Here is the error:

    CC unittests/oslib/strcasestr.o
    CC unittests/oslib/strsep.o
  LINK fio
ld.lld: error: undefined symbol: static_tv_valid
>>> referenced by gettime.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Rishabh Shukla investigated and found that clang + ld builds
successfully. So the problem seems to be with lld 16.0.0-1.

Until we find the root cause let's just disable __thread support on
AppVeyor msys2 builds.

Link: https://github.com/axboe/fio/issues/1559
Suggested-by: Rishabh Shukla <rishabh.sh@samsung.com>
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>