Disable cpuinfo for ARM64EC builds. (microsoft#25831)

### Description
<!-- Describe your changes. -->

Disable cpuinfo for ARM64EC builds. There's an error when linking to
cpuinfo built for ARM64EC when using `--use_vckpg`.

This issue was exposed by a recent change (microsoft#25228) but cpuinfo was
actually not being used before for ARM64EC. The macros here don't
properly account for ARM64EC:

https://github.com/microsoft/onnxruntime/blob/e6d3e085cb0bb96da7c3458b97316ecca234b37a/onnxruntime/core/common/cpuid_arch_definition.h#L8-L14

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

Fix a packaging pipeline failure. Revert to the old behavior of not
calling cpuinfo from the CPUIDInfo ctor for ARM64EC.

This PR is just a workaround. The cpuinfo link issue needs more
investigation.

Author: edgchen1

cmake/external/onnxruntime_external_deps.cmake

@@ -331,7 +331,13 @@ if (onnxruntime_ENABLE_CPUINFO)
       set(CPUINFO_SUPPORTED TRUE)
     endif()
     if (WIN32)
-      set(CPUINFO_SUPPORTED TRUE)
+      # There's an error when linking with cpuinfo on arm64ec with a vcpkg build (--use_vcpkg).
+      # TODO Fix it and then re-enable cpuinfo on arm64ec.
+      if (onnxruntime_target_platform STREQUAL "ARM64EC")
+        set(CPUINFO_SUPPORTED FALSE)
+      else()
+        set(CPUINFO_SUPPORTED TRUE)
+      endif()
     elseif (NOT ${onnxruntime_target_platform} MATCHES "^(i[3-6]86|AMD64|x86(_64)?|armv[5-8].*|aarch64|arm64)$")
       message(WARNING
         "Target processor architecture \"${onnxruntime_target_platform}\" is not supported in cpuinfo. "