Features/Meson

What's next?

Blockers for further conversions

Complete moving installation rules to meson.build: Marc-André and Paolo already have patches for this. You're welcome to propose yourself for helping!; Benefit: allows removing parts of Makefile, leaving it as just an orchestrator for submodules, Makefile.ninja and Makefile.mtest
Complete moving build rules to meson.build: Move the build rules from tests/Makefile.include to tests/meson.build. You can take inspiration from tests/qtest/Makefile.include; Benefit: allows removing CFLAGS, LDFLAGS, LIBS and LIBS_SOFTMMU, as well as most if not all of rules.mak.

Move pkg-config tests to meson.build: Replace declare_dependency statements with dependency statements; Benefit: allows removing *_CFLAGS and *_LIBS variables from config-host.mak. Allows using dependency objects instead of CONFIG_* symbols when declaring sourcesets.
Change simple config-host.mak symbols to Meson options: Some symbols (e.g. CONFIG_PARALLELS) are only used placed in config-host.mak to be read from Meson. Instead pass them through -D... command-line options; Benefit: allows removing CONFIG_* variables from config-host.mak.

Include config-target.mak files in the tree: Remove the configuration loop in configure and just include the content of the .mak files directly in the tree, for example in a target/configs/ directory. (There are some small complications because config-target.mak file currently includes the host disassembler symbols too, e.g. CONFIG_I386_DIS).; Benefit: remove large swaths of imperative code, remove *-linux-user and *-softmmu directories from the build tree.
Move other compile tests from configure to meson.build