add a test combining Windows + Visual + Clang-Cl + DISPATCH=1

[Cyan4973]

test that #763 is fixed and remains fixed

[t-mat]

https://github.com/Cyan4973/xxHash/actions/runs/5562735680/jobs/10161223314?pr=863#step:7:15

Since we don't see the "Enable xxHash dispatch mode" message from the following block, it seems it doesn't work properly.

xxHash/cmake_unofficial/CMakeLists.txt

Lines 88 to 94 in 4fd75d7

	if("${PLATFORM}" STREQUAL "x86_64")
	message(STATUS "Enable xxHash dispatch mode")
	add_library(xxhash "${XXHASH_DIR}/xxh_x86dispatch.c"
	"${XXHASH_DIR}/xxhash.c"
	)
	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DXXHSUM_DISPATCH=1")
	else()

[Cyan4973]

mmmh, that doesn't work.
The generated xxhsum binary still doesn't use DISPATCH despite setting -DDISPATCH=1 at cmake build time.

Strangely, the same command seems to work fine in local tests on Ubuntu.
So maybe this could be related to the Windows + Visual Studio environment (?)

[t-mat]

It seems the actual Architecture (${PLATFORM}) for MSVC x86_64 is AMD64

https://github.com/Cyan4973/xxHash/actions/runs/5562735680/jobs/10161223314?pr=863#step:7:22

-- Detecting C compile features - done
-- Architecture: AMD64
-- Configuring done (2.5s)

The following patch for cmake_unofficial/CMakeList.txt enables dispatch mode for clang-cl.

# Only support DISPATCH option on x86_64.
- if("${PLATFORM}" STREQUAL "x86_64")
+ if(("${PLATFORM}" STREQUAL "x86_64") OR ("${PLATFORM}" STREQUAL "AMD64"))

But it may cause error. See also #763 (comment)

[t-mat]

After #865, this PR should work properly.

[Cyan4973]

rebasing on top of @t-mat 's #865

[Cyan4973]

This works great ! Thanks @t-mat !

The test will now also properly fail with a clear error signal if the produced xxhsum binary is not autoVec.

[t-mat]

https://github.com/Cyan4973/xxHash/actions/runs/5564095301/jobs/10163482759#step:7:25

-- Enable xxHash dispatch mode

https://github.com/Cyan4973/xxHash/actions/runs/5564095444/jobs/10163482094?pr=863#step:8:7

compiled as 64-bit x86_64 autoVec little endian with Clang 12.0.0  

🥳