diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -133,7 +133,8 @@
 
 set(LIBCXXABI_LIBCXX_INCLUDES "" CACHE PATH
     "Specify path to libc++ includes.")
-if (NOT libcxx IN_LIST LLVM_ENABLE_RUNTIMES)
+# FIXME checking two lists to support different sorts of builds is bad.
+if ((NOT libcxx IN_LIST LLVM_ENABLE_RUNTIMES) AND (NOT libcxx IN_LIST LLVM_ENABLE_PROJECTS))
   if (NOT IS_DIRECTORY ${LIBCXXABI_LIBCXX_INCLUDES})
     message(FATAL_ERROR
       "LIBCXXABI_LIBCXX_INCLUDES=${LIBCXXABI_LIBCXX_INCLUDES} is not a valid directory. "
diff --git a/libcxxabi/test/CMakeLists.txt b/libcxxabi/test/CMakeLists.txt
--- a/libcxxabi/test/CMakeLists.txt
+++ b/libcxxabi/test/CMakeLists.txt
@@ -61,10 +61,11 @@
   list(APPEND LIBCXXABI_TEST_DEPS cxx_external_threads)
 endif()
 
-if(libcxx IN_LIST LLVM_ENABLE_RUNTIMES)
+# FIXME checking two lists to support different sorts of builds is bad.
+if (libcxx IN_LIST LLVM_ENABLE_RUNTIMES OR libcxx IN_LIST LLVM_ENABLE_PROJECTS)
   list(APPEND LIBCXXABI_TEST_DEPS cxx)
 endif()
-if(libunwind IN_LIST LLVM_ENABLE_RUNTIMES)
+if (libunwind IN_LIST LLVM_ENABLE_RUNTIMES OR libunwind IN_LIST LLVM_ENABLE_PROJECTS)
   if (LIBCXXABI_USE_LLVM_UNWINDER AND TARGET unwind)
     list(APPEND LIBCXXABI_TEST_DEPS unwind)
   endif()
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -125,7 +125,7 @@
   if (${proj} IN_LIST LLVM_ENABLE_PROJECTS)
     # TODO(Ericson2314): Making non-fatal for now because of out-of-tree docs
     # CI jobs use this.
-    message(SEND_ERROR
+    message(WARNING
       "Using LLVM_ENABLE_PROJECTS=${proj} is incorrect. Please use -DLLVM_ENABLE_RUNTIMES=${proj} or "
       "see the instructions at https://libcxx.llvm.org/BuildingLibcxx.html for building the runtimes.")
   endif()