[clangd] Add target_info test

[kadircet]

• Only test for arm

[kadircet]

landed as 101a69d71b93f901561621508ed36b187e594d91

clang-tools-extra/clangd/test/target_info.test

+# REQUIRES: arm-registered-target
+# Mock 'compile_commands.json' to contain a driver name targeting armv7.
+# Afterwards check that correct target is passed into clang.
+
+# RUN: rm -rf %t.dir && mkdir -p %t.dir
+
+# RUN: echo '[{"directory": "%/t.dir", "command": "%/t.dir/armv7-clang -x c++ the-file.cpp -v", "file": "the-file.cpp"}]' > %t.dir/compile_commands.json
+
+# RUN: sed -e "s|INPUT_DIR|%/t.dir|g" %s > %t.test.1
+# On Windows, we need the URI in didOpen to look like "uri":"file:///C:/..."
+# (with the extra slash in the front), so we add it here.
+# RUN: sed -E -e "s|file://([A-Z]):/|file:///\1:/|g" %t.test.1 > %t.test
+
+# RUN: clangd -lit-test < %t.test 2>&1 | FileCheck -strict-whitespace %t.test
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{}}
+---
+{
+  "jsonrpc":"2.0",
+  "method":"textDocument/didOpen",
+  "params": {
+    "textDocument": {
+      "uri": "file://INPUT_DIR/the-file.cpp",
+      "languageId":"cpp",
+      "version":1,
+      "text":""
+    }
+  }
+}
+# Make sure we have target passed into cc1 driver, which is printed due to -v in
+# the compile_commands.json
+# CHECK: Target: armv7
+---
+{"jsonrpc":"2.0","id":10000,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}