Add modified runtimes back to runtimes_to_{test|build} (#145805)

Add libc back into the runtimes_to_test since other runtimes were
removed.

.ci/compute_projects.py

@@ -77,6 +77,7 @@ DEPENDENT_RUNTIMES_TO_BUILD = {"lldb": {"libcxx", "libcxxabi", "libunwind"}}
 DEPENDENT_RUNTIMES_TO_TEST = {
     "clang": {"compiler-rt"},
     "clang-tools-extra": {"libc"},
+    "libc": {"libc"},
     ".ci": {"compiler-rt", "libc"},
 }
 DEPENDENT_RUNTIMES_TO_TEST_NEEDS_RECONFIG = {

.ci/compute_projects_test.py

@@ -187,7 +187,7 @@ class TestComputeProjects(unittest.TestCase):
         self.assertEqual(env_variables["runtimes_check_targets"], "")
         self.assertEqual(env_variables["runtimes_check_targets_needs_reconfig"], "")
 
-    def test_exclude_runtiems_in_projects(self):
+    def test_exclude_libcxx_in_projects(self):
         env_variables = compute_projects.get_env_variables(
             ["libcxx/CMakeLists.txt"], "Linux"
         )
@@ -197,6 +197,16 @@ class TestComputeProjects(unittest.TestCase):
         self.assertEqual(env_variables["runtimes_check_targets"], "")
         self.assertEqual(env_variables["runtimes_check_targets_needs_reconfig"], "")
 
+    def test_include_libc_in_runtimes(self):
+        env_variables = compute_projects.get_env_variables(
+            ["libc/CMakeLists.txt"], "Linux"
+        )
+        self.assertEqual(env_variables["projects_to_build"], "clang;lld")
+        self.assertEqual(env_variables["project_check_targets"], "")
+        self.assertEqual(env_variables["runtimes_to_build"], "libc")
+        self.assertEqual(env_variables["runtimes_check_targets"], "check-libc")
+        self.assertEqual(env_variables["runtimes_check_targets_needs_reconfig"], "")
+
     def test_exclude_docs(self):
         env_variables = compute_projects.get_env_variables(
             ["llvm/docs/CIBestPractices.rst"], "Linux"