MesonToolchain reads conf tools.build:defines

[franramirez688]

Changelog: Bugfix: Make MesonToolchain listen to tools.build:defines conf variable.
Docs: conan-io/docs#3709
Closes: #16169

[paulharris]

Did you also update the docs?
Specifically:

here (does not mention tools.build:defines)
https://docs.conan.io/2/reference/tools/meson/mesontoolchain.html#conf

And here:
https://docs.conan.io/2/reference/config_files/global_conf.html

tools.build:cxxflags: List of extra CXX flags used by different toolchains like CMakeToolchain, AutotoolsToolchain and MesonToolchain
tools.build:defines: List of extra definition flags used by different toolchains like CMakeToolchain and AutotoolsToolchain

It does not mention MesonToolchain in the list of toolchains - Meson IS mentioned in cxxflags, so it should also be mentioned in defines.