[bug] x86 build reports CMAKE_SYSTEM_PROCESSOR=AMD64 and not i386

### Describe the bug

Hi,

When buidling a x86 project (Have seen it on windows but based on my research probably also on other OS-es), the CMAKE_SYSTEM_NAME reports a 64 bit architecture.

Reason is this [code exception here](https://github.com/conan-io/conan/blob/709ef11aee236bf8e2165c4af86f3da6a1af9235/conan/tools/cmake/toolchain/blocks.py#L1018C1-L1018C73). CMAKE_SYSTEM_NAME is not set, therefore processor is neither set by conan nor by CMake internas. Note that CMake does only try to find the real TARGET processor name when [CMAKE_SYSTEM_NAME is set](https://github.com/Kitware/CMake/blob/master/Modules/CMakeDetermineSystem.cmake#L156), but always uses CMAKE_HOST_SYSTEM_PROCESSOR when it is not set.

This does not affect compilation results, but decisions made based on that variable (e.g. folder names).

Workaround:
- Set CMAKE_SYSTEM_NAME in profile or toolchain e.g: `tools.cmake.cmaketoolchain:system_name=Windows`
- (Optional) Disable CMAKE_CROSSCOPILING. Otherwise CMake will not try to execute your created binaries. See [add_custom_command](https://cmake.org/cmake/help/latest/command/add_custom_command.html)

Btw, a little rant about jargon. I dislike the conan build/host naming. It is really counterintuitive when coming from CMake only projects... Example:

| conan | cmake |
|--------|--------|
| arch_build | CMAKE_HOST_SYSTEM_PROCESSOR |
| arch_host | CMAKE_SYSTEM_PROCESSOR |

### How to reproduce it

Run this example project and a windows x86 profile:

conanfile.py
```
from conan import ConanFile
from conan.tools.cmake import CMake, cmake_layout

class Recipe(ConanFile):
name = "cmake_test"
version = "1.0"
settings = "os", "build_type"
generators = "CMakeToolchain"

def layout(self):
cmake_layout(self)

def build(self):
cmake = CMake(self)
cmake.configure()
```

CMakeLists.txt
```
cmake_minimum_required(VERSION 3.15)
project(foo LANGUAGES NONE)
message(STATUS "CMAKE_SYSTEM_PROCESSOR: ${CMAKE_SYSTEM_PROCESSOR}")
```

profile
```
[settings]
arch=x86
os=Windows
...
```