diff --git a/llvm/cmake/modules/LLVMInstallSymlink.cmake b/llvm/cmake/modules/LLVMInstallSymlink.cmake
--- a/llvm/cmake/modules/LLVMInstallSymlink.cmake
+++ b/llvm/cmake/modules/LLVMInstallSymlink.cmake
@@ -2,6 +2,9 @@
 # DESTDIR environment variable may be unset at configuration time.
 # See PR8397.
 
+# Set to an arbitrary directory to silence GNUInstallDirs warnings
+# regarding being unable to determine libdir.
+set(CMAKE_INSTALL_LIBDIR "lib")
 include(GNUInstallDirs)
 
 function(install_symlink name target outdir)