diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -260,13 +260,19 @@
   function(builtin_default_target compiler_rt_path)
     cmake_parse_arguments(ARG "" "" "DEPENDS" ${ARGN})
 
+    set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default ON)
+    # AIX should fold 32-bit & 64-bit arch libraries into a single archive.
+    if (TARGET_TRIPLE MATCHES "aix")
+      set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
+    endif()
+
     llvm_ExternalProject_Add(builtins
                              ${compiler_rt_path}/lib/builtins
                              DEPENDS ${ARG_DEPENDS}
                              CMAKE_ARGS -DLLVM_LIBRARY_OUTPUT_INTDIR=${LLVM_LIBRARY_DIR}
                                         -DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_TOOLS_BINARY_DIR}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
-                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_C_COMPILER_WORKS=ON
@@ -400,6 +406,12 @@
       list(APPEND test_targets runtimes-test-depends check-runtimes)
     endif()
 
+    set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default ON)
+    # AIX should fold 32-bit & 64-bit arch libraries into a single archive.
+    if (TARGET_TRIPLE MATCHES "aix")
+      set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
+    endif()
+
     llvm_ExternalProject_Add(runtimes
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${ARG_DEPENDS} ${CXX_HEADER_TARGET}
@@ -408,7 +420,7 @@
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
                                         -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
-                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_CXX_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}