diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -144,7 +144,10 @@
 endif()
 
 # Select the runtimes to build
-set(LLVM_DEFAULT_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp")
+#
+# As we migrate runtimes to using the bootstrapping build, the set of default runtimes
+# should grow as we remove those runtimes from LLVM_ENABLE_PROJECTS above.
+set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")
 set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")