[llvm] [Dexter] Add basic structured script parsing (PR #193710)

[Stephen Tozer via llvm-commits]

================
@@ -223,16 +266,24 @@ def can_target_host():
 # Dexter tests run on the host machine. If the host arch is supported add
 # 'dexter' as an available feature and force the dexter tests to use the host
 # triple.
-if can_target_host():
-    if config.host_triple != config.target_triple:
-        print("Forcing dexter tests to use host triple {}.".format(config.host_triple))
-    dependencies = configure_dexter_substitutions()
-    if all(d in config.available_features for d in dependencies):
-        config.available_features.add("dexter")
+if check_dexter_requirements():
----------------
SLTozer wrote:

We can't early exit here, since this isn't in a function - so we could only exit the whole script early. I can invert the conditions though such that we don't have to use nested ifs.

https://github.com/llvm/llvm-project/pull/193710