[clangd][test] Provide registered targets to lit tests

Summary:
We had tests in clangd (target_info.test) that got enabled only on
systems that know about x86. But they were always disabled as clangd lit config
never registered those targets.

This patch adds those targets as `$TARGET$-registered-target`

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77944

clang-tools-extra/clangd/test/lit.cfg.py

@@ -10,10 +10,19 @@ config.test_format = lit.formats.ShTest(not lit.llvm.llvm_config.use_lit_shell)
 config.test_source_root = config.clangd_source_dir + "/test"
 config.test_exec_root = config.clangd_binary_dir + "/test"
 
+
+# Used to enable tests based on the required targets. Can be queried with e.g.
+#    REQUIRES: x86-registered-target
+def calculate_arch_features(arch_string):
+  return [arch.lower() + '-registered-target' for arch in arch_string.split()]
+
+
+lit.llvm.llvm_config.feature_config([('--targets-built',
+                                      calculate_arch_features)])
+
 # Clangd-specific lit environment.
 config.substitutions.append(('%clangd-benchmark-dir',
                              config.clangd_binary_dir + "/benchmarks"))
 
 if config.clangd_build_xpc:
   config.available_features.add('clangd-xpc-support')
-