Try to better detect host arch under FreeBSD

Author: Szczepan

eng/native/configureplatform.cmake

@@ -160,12 +160,12 @@ endif(CLR_CMAKE_HOST_OS STREQUAL Android)
 
 if(CLR_CMAKE_HOST_OS STREQUAL FreeBSD)
     set(CLR_CMAKE_HOST_UNIX 1)
-    if (CMAKE_SYSTEM_PROCESSOR STREQUAL amd64)
+    if (CMAKE_SYSTEM_PROCESSOR STREQUAL amd64 OR CMAKE_SYSTEM_PROCESSOR STREQUAL x86_64)
         set(CLR_CMAKE_HOST_UNIX_AMD64 1)
-    elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64)
+    elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64 OR CMAKE_SYSTEM_PROCESSOR STREQUAL arm64)
         set(CLR_CMAKE_HOST_UNIX_ARM64 1)
     else()
-        message(FATAL_ERROR "Unknown FreeBSD processor architecture")
+        clr_unknown_arch()
     endif()
     set(CLR_CMAKE_HOST_FREEBSD 1)
 endif(CLR_CMAKE_HOST_OS STREQUAL FreeBSD)