fix amd64 support (#223)

Fix when "${CMAKE_SYSTEM_PROCESSOR}" is lowercase "amd64"

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Co-authored-by: David Nadoba <d_nadoba@apple.com>
Co-authored-by: David Nadoba <dnadoba@gmail.com>

cmake/modules/SwiftSupport.cmake

@@ -40,7 +40,7 @@ function(get_swift_host_arch result_var_name)
     set("${result_var_name}" "armv7" PARENT_SCOPE)
   elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv7-a")
     set("${result_var_name}" "armv7" PARENT_SCOPE)
-  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "AMD64")
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "AMD64|amd64")
     set("${result_var_name}" "x86_64" PARENT_SCOPE)
   elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "IA64")
     set("${result_var_name}" "itanium" PARENT_SCOPE)