diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -272,9 +272,15 @@
 
 # Target options --------------------------------------------------------------
 option(LIBCXX_BUILD_32_BITS "Build 32 bit libc++." ${LLVM_BUILD_32_BITS})
-set(LIBCXX_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
-set(LIBCXX_SYSROOT "" CACHE STRING "Use alternate sysroot.")
-set(LIBCXX_GCC_TOOLCHAIN "" CACHE STRING "Use alternate GCC toolchain.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXX_TARGET_TRIPLE "${LIBCXX_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
+set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}" CACHE STRING "Use alternate sysroot.")
+set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE STRING "Use alternate GCC toolchain.")
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_ENABLE_EXCEPTIONS "Use exceptions." ON)
@@ -486,21 +492,14 @@
 # 'config-ix' use them during feature checks. It also adds them to both
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
 add_target_flags_if(LIBCXX_BUILD_32_BITS "-m32")
-
 if(LIBCXX_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXX_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBCXX_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXX_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 
 # Configure compiler.
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -113,9 +113,16 @@
 set(LIBCXXABI_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXXABI_INSTALL_LIBRARY "Install the libc++abi library." ON)
-set(LIBCXXABI_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBCXXABI_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXXABI_TARGET_TRIPLE "${LIBCXXABI_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
+
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \
@@ -271,18 +278,12 @@
 
 if(LIBCXXABI_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXXABI_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBCXXABI_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
-if(LIBCXX_GCC_TOOLCHAIN)
+if(LIBCXXABI_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXXABI_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBCXXABI_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler. Must happen after setting the target flags.
diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -80,9 +80,14 @@
 cmake_dependent_option(LIBUNWIND_INSTALL_SHARED_LIBRARY
   "Install the shared libunwind library." ON
   "LIBUNWIND_ENABLE_SHARED;LIBUNWIND_INSTALL_LIBRARY" OFF)
-set(LIBUNWIND_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBUNWIND_TARGET_TRIPLE "${LIBUNWIND_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
 set(LIBUNWIND_TEST_LINKER_FLAGS "" CACHE STRING
     "Additional linker flags for test programs.")
 set(LIBUNWIND_TEST_COMPILER_FLAGS "" CACHE STRING
@@ -170,18 +175,12 @@
 
 if(LIBUNWIND_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBUNWIND_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBUNWIND_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBUNWIND_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBUNWIND_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBUNWIND_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler.