accel: Re-enable WHPX cross-build on case sensitive filesystems

accel: Re-enable WHPX cross-build on case sensitive filesystems

Since MinGW commit 395dcfdea ("rename hyper-v headers and def
files to lower case") [*], WinHvPlatform.h and WinHvEmulation.h
got respectively renamed as winhvplatform.h / winhvemulation.h.

The mingw64-headers package included in the Fedora version we
use for CI does include this commit; and meson fails to detect
these present-but-renamed headers while cross-building (on
case-sensitive filesystems).

Use the renamed header in order to detect and successfully
cross-build with the WHPX accelerator.

Note, on Windows hosts, the libraries are still named as
WinHvPlatform.dll and WinHvEmulation.dll, so we don't bother
renaming the definitions used by load_whp_dispatch_fns() in
target/i386/whpx/whpx-all.c.

[*] https://sourceforge.net/p/mingw-w64/mingw-w64/ci/395dcfdea

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230624142211.8888-3-philmd@linaro.org>