Use 64bit build on `CMAKE_SYSTEM_PROCESSOR=i386` on Darwin

Here a bit tricky things.

A value `CMAKE_SYSTEM_PROCESSOR` is came from output of `uname -m` which
migth be 32bit with 64bit building applicaiton.

So, for that case use `CMAKE_SIZEOF_VOID_P` to detect the target.

See https://trac.macports.org/ticket/68488

cmake/system_check.cmake

@@ -46,7 +46,7 @@ elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "loongarch64.*")
   set(LOONGARCH64 1)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "riscv64.*")
   set(RISCV64 1)
-elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "amd64.*|x86_64.*|AMD64.*")
+elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "amd64.*|x86_64.*|AMD64.*" OR (CMAKE_SYSTEM_NAME MATCHES "Darwin" AND CMAKE_SYSTEM_PROCESSOR MATCHES "i686.*|i386.*|x86.*"))
   if (NOT BINARY)
     if("${CMAKE_SIZEOF_VOID_P}" EQUAL "8")
       set(X86_64 1)