Make `PerMachine` and `MachineChoice` have just `build` and `host`

Meson itself *almost* only cares about the build and host platforms. The
exception is it takes a `target_machine` in the cross file and exposes
it to the user; but it doesn't do anything else with it. It's therefore
overkill to put target in `PerMachine` and `MachineChoice`. Instead, we
make a `PerThreeMachine` only for the machine infos.

Additionally fix a few other things that were bugging me in the process:

 - Get rid of `MachineInfos` class. Since `envconfig.py` was created, it
   has no methods that couldn't just got on `PerMachine`

 - Make `default_missing` and `miss_defaulting` work functionally. That
   means we can just locally bind rather than bind as class vars the
   "unfrozen" configuration. This helps prevent bugs where one forgets
   to freeze a configuration.

1 files changed, 1 insertions, 1 deletions

diff --git a/run_tests.py b/run_tests.py
index a4b0fa2..f427736 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -220,7 +220,7 @@ def clear_meson_configure_class_caches():
     mesonbuild.compilers.CCompiler.find_library_cache = {}
     mesonbuild.compilers.CCompiler.find_framework_cache = {}
     mesonbuild.dependencies.PkgConfigDependency.pkgbin_cache = {}
-    mesonbuild.dependencies.PkgConfigDependency.class_pkgbin = mesonlib.PerMachine(None, None, None)
+    mesonbuild.dependencies.PkgConfigDependency.class_pkgbin = mesonlib.PerMachine(None, None)
 
 def run_configure_inprocess(commandlist):
     old_stdout = sys.stdout