diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index b89cd4981a721..bf3601cb312fd 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -203,8 +203,16 @@ impl Step for Llvm {
             cfg.define("LLVM_BUILD_32_BITS", "ON");
         }
 
+        let mut enabled_llvm_projects = Vec::new();
+
+        if util::forcing_clang_based_tests() {
+            enabled_llvm_projects.push("clang");
+            enabled_llvm_projects.push("compiler-rt");
+        }
+
         if want_lldb {
-            cfg.define("LLVM_ENABLE_PROJECTS", "clang;lldb;compiler-rt");
+            enabled_llvm_projects.push("clang");
+            enabled_llvm_projects.push("lldb");
             // For the time being, disable code signing.
             cfg.define("LLDB_CODESIGN_IDENTITY", "");
             cfg.define("LLDB_NO_DEBUGSERVER", "ON");
@@ -214,6 +222,12 @@ impl Step for Llvm {
             cfg.define("LLVM_ENABLE_LIBXML2", "OFF");
         }
 
+        if enabled_llvm_projects.len() > 0 {
+            enabled_llvm_projects.sort();
+            enabled_llvm_projects.dedup();
+            cfg.define("LLVM_ENABLE_PROJECTS", enabled_llvm_projects.join(";"));
+        }
+
         if let Some(num_linkers) = builder.config.llvm_link_jobs {
             if num_linkers > 0 {
                 cfg.define("LLVM_PARALLEL_LINK_JOBS", num_linkers.to_string());
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 05b3ce6bc8964..9d0aa09f15cfb 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1143,24 +1143,9 @@ impl Step for Compiletest {
             }
         }
 
-        if let Some(var) = env::var_os("RUSTBUILD_FORCE_CLANG_BASED_TESTS") {
-            match &var.to_string_lossy().to_lowercase()[..] {
-                "1" | "yes" | "on" => {
-                    assert!(builder.config.lldb_enabled,
-                        "RUSTBUILD_FORCE_CLANG_BASED_TESTS needs Clang/LLDB to \
-                         be built.");
-                    let clang_exe = builder.llvm_out(target).join("bin").join("clang");
-                    cmd.arg("--run-clang-based-tests-with").arg(clang_exe);
-                }
-                "0" | "no" | "off" => {
-                    // Nothing to do.
-                }
-                other => {
-                    // Let's make sure typos don't get unnoticed
-                    panic!("Unrecognized option '{}' set in \
-                            RUSTBUILD_FORCE_CLANG_BASED_TESTS", other);
-                }
-            }
+        if util::forcing_clang_based_tests() {
+            let clang_exe = builder.llvm_out(target).join("bin").join("clang");
+            cmd.arg("--run-clang-based-tests-with").arg(clang_exe);
         }
 
         // Get paths from cmd args
diff --git a/src/bootstrap/util.rs b/src/bootstrap/util.rs
index f22f0559265b1..9f684678bb060 100644
--- a/src/bootstrap/util.rs
+++ b/src/bootstrap/util.rs
@@ -356,3 +356,19 @@ impl CiEnv {
         }
     }
 }
+
+pub fn forcing_clang_based_tests() -> bool {
+    if let Some(var) = env::var_os("RUSTBUILD_FORCE_CLANG_BASED_TESTS") {
+        match &var.to_string_lossy().to_lowercase()[..] {
+            "1" | "yes" | "on" => true,
+            "0" | "no" | "off" => false,
+            other => {
+                // Let's make sure typos don't go unnoticed
+                panic!("Unrecognized option '{}' set in \
+                        RUSTBUILD_FORCE_CLANG_BASED_TESTS", other)
+            }
+        }
+    } else {
+        false
+    }
+}