compiler_executables emulator key

[perseoGI]

Changelog: Feature: compiler_executables admit new emulator key which can control Meson exe_wrapper and CMake CMAKE_CROSSCOMPILING_EMULATOR
Docs: TODO

Close #18718
Close #19912

Related PR: #19983

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• Refer to the issue that supports this Pull Request.
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
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[AbrilRBS]

This is outside my knowledge, will let someone else weight in on it

[franramirez688]

It's looking great! I left a couple of comments to be discussed, basically:

• I think that we do not really need a public argument to define the wrapper, as any recipe should not define it via the generate() function.
• I think that the only change could be this https://github.com/conan-io/conan/pull/19940/changes#r3235881460
• Instead of self._emulator as an attribute in the toolchain, let's name it self._exe_wrapper. I think it's clearer.

[franramirez688]

The only change to add could be something like:

        #: Defines the Meson ``objcpp_link_args`` variable. Defaulted to ``LDFLAGS`` build environment value
        self.objcpp_link_args = []
        # Let's check if any emulator was defined
        self._exe_wrapper = None
        exe_wrapper = compilers_by_conf.get("emulator")
        if native is False and is_cross_building and exe_wrapper:
            self._exe_wrapper = exe_wrapper
            self.properties["needs_exe_wrapper"] = True

[perseoGI]

I understand, I've changed the property name.
And to avoid duplicating the if native is False and is_cross_building and exe_wrapper logic, I've moved the read of compilers_by_conf upper, so that we can maintain the needs_exe_wrapper logic wher it was

[franramirez688]

This is wrong as it's only used for cross-compiling and native=False. That's why I'm proposing this https://github.com/conan-io/conan/pull/19940/changes#r3235881460

[memsharded]

Does this have an equivalent for CMake? It would be good to see its application for CMake too.