Index: compiler-rt/cmake/base-config-ix.cmake
===================================================================
--- compiler-rt/cmake/base-config-ix.cmake
+++ compiler-rt/cmake/base-config-ix.cmake
@@ -153,7 +153,7 @@
   option(COMPILER_RT_DEFAULT_TARGET_ONLY "Build builtins only for the default target" Off)
 endif()
 
-if(WIN32 AND NOT MINGW AND NOT CYGWIN)
+if(MSVC)
   set(CMAKE_SHARED_LIBRARY_PREFIX_C "")
   set(CMAKE_SHARED_LIBRARY_PREFIX_CXX "")
   set(CMAKE_STATIC_LIBRARY_PREFIX_C "")
Index: llvm/runtimes/CMakeLists.txt
===================================================================
--- llvm/runtimes/CMakeLists.txt
+++ llvm/runtimes/CMakeLists.txt
@@ -63,19 +63,12 @@
 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 (LLVM_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=${LLVM_TOOLS_BINARY_DIR}
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
-                                      -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
@@ -219,12 +212,6 @@
     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 (LLVM_TARGET_TRIPLE MATCHES "aix")
-    set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
-  endif()
-
   llvm_ExternalProject_Add(runtimes
                            ${CMAKE_CURRENT_SOURCE_DIR}/../../runtimes
                            DEPENDS ${ARG_DEPENDS}
@@ -233,7 +220,6 @@
                                       -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
                                       -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
-                                      -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                       -DLLVM_BUILD_TOOLS=${LLVM_BUILD_TOOLS}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON