The top level CMakeLists.txt should call enable_language(ASM_MARMASM) on Windows

CMake has multiple ASM dialects. For example, ASM, ASM_MASM and ASM_MARMASM.
On Posix platforms you should use ASM, which uses an AT&T style assembly syntax that `gas` uses.
On Windows you need to use MASM, which has two dialects: ASM_MASM and ASM_MARMASM.
ASM_MASM is for Intel x86. ASM_MARMASM is for ARM.

You may change `PROJECT(XNNPACK C CXX ASM)` to:
```cmake
PROJECT(XNNPACK C CXX)
if (MSVC)
if (CMAKE_VS_PLATFORM_NAME)
# Multi-platform generator
set(xnnpack_target_platform ${CMAKE_VS_PLATFORM_NAME})
else()
set(xnnpack_target_platform ${CMAKE_SYSTEM_PROCESSOR})
endif()
if (xnnpack_target_platform STREQUAL "ARM64")
set(xnnpack_target_platform "ARM64")
enable_language(ASM_MARMASM)
elseif (xnnpack_target_platform STREQUAL "ARM64EC")
enable_language(ASM_MARMASM)
elseif (xnnpack_target_platform STREQUAL "ARM" OR CMAKE_GENERATOR MATCHES "ARM")
set(xnnpack_target_platform "ARM")
enable_language(ASM_MARMASM)
elseif (xnnpack_target_platform STREQUAL "x64" OR xnnpack_target_platform STREQUAL "x86_64" OR xnnpack_target_platform STREQUAL "AMD64" OR CMAKE_GENERATOR MATCHES "Win64")
set(xnnpack_target_platform "x64")
enable_language(ASM_MASM)
elseif (xnnpack_target_platform STREQUAL "Win32" OR xnnpack_target_platform STREQUAL "x86" OR xnnpack_target_platform STREQUAL "i386" OR xnnpack_target_platform STREQUAL "i686")
set(xnnpack_target_platform "x86")
enable_language(ASM_MASM)
else()
message(FATAL_ERROR "Unknown CMAKE_SYSTEM_PROCESSOR: ${CMAKE_SYSTEM_PROCESSOR}")
endif()
else()
enable_language(ASM)
endif()
```
See:
 1. https://cmake.org/cmake/help/latest/envvar/ASM_DIALECT.html
 2. https://gitlab.kitware.com/cmake/cmake/-/issues/26617