Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -55,6 +55,7 @@
 set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
+option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
 
 # ABI Library options ---------------------------------------------------------
@@ -94,6 +95,23 @@
 set(LIBCXX_COVERAGE_LIBRARY "" CACHE STRING
     "The Profile-rt library used to build with code coverage")
 
+# Don't allow a user to accidentally overwrite the system libc++ installation on Darwin.
+# If the user specifies -DCMAKE_INSTALL_PREFIX=/usr the install rules for libc++
+# will not be generated and a warning will be issued.
+option(LIBCXX_OVERRIDE_DARWIN_INSTALL "Enable overwriting darwins libc++ installation." OFF)
+mark_as_advanced(LIBCXX_OVERRIDE_DARWIN_INSTALL) # Don't show this option by default.
+
+if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT LIBCXX_OVERRIDE_DARWIN_INSTALL)
+  if ("${CMAKE_INSTALL_PREFIX}" STREQUAL "/usr")
+    message(WARNING "Disabling libc++ install rules because installation would "
+                    "overwrite the systems installation. Configure with "
+                    "-DLIBCXX_OVERRIDE_DARWIN_INSTALL=ON to suppress this behaviour.")
+    mark_as_advanced(CLEAR LIBCXX_OVERRIDE_DARWIN_INSTALL) # Show the override option.
+    set(LIBCXX_INSTALL_HEADERS OFF)
+    set(LIBCXX_INSTALL_LIBRARY OFF)
+  endif()
+endif()
+
 #===============================================================================
 # Check option configurations
 #===============================================================================
Index: cmake/Modules/HandleLibCXXABI.cmake
===================================================================
--- cmake/Modules/HandleLibCXXABI.cmake
+++ cmake/Modules/HandleLibCXXABI.cmake
@@ -41,11 +41,13 @@
         file(COPY "${incpath}/${fpath}"
           DESTINATION "${CMAKE_BINARY_DIR}/include/${dstdir}"
           )
-        install(FILES "${CMAKE_BINARY_DIR}/include/${fpath}"
-          DESTINATION include/c++/v1/${dstdir}
-          COMPONENT libcxx
-          PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-          )
+        if (LIBCXX_INSTALL_HEADERS)
+          install(FILES "${CMAKE_BINARY_DIR}/include/${fpath}"
+            DESTINATION include/c++/v1/${dstdir}
+            COMPONENT libcxx
+            PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+            )
+        endif()
         list(APPEND abilib_headers "${CMAKE_BINARY_DIR}/include/${fpath}")
       endif()
     endforeach()
Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -133,15 +133,18 @@
     SOVERSION     "1"
   )
 
-install(TARGETS cxx
-  LIBRARY DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
-  ARCHIVE DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
-  )
+if (LIBCXX_INSTALL_LIBRARY)
+  install(TARGETS cxx
+    LIBRARY DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
+    ARCHIVE DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
+    )
+endif()
 
-if (NOT CMAKE_CONFIGURATION_TYPES)
-  add_custom_target(install-libcxx
-                    DEPENDS cxx
-                    COMMAND "${CMAKE_COMMAND}"
-                    -DCMAKE_INSTALL_COMPONENT=libcxx
-                    -P "${LIBCXX_BINARY_DIR}/cmake_install.cmake")
+if (NOT CMAKE_CONFIGURATION_TYPES AND (LIBCXX_INSTALL_LIBRARY OR
+                                       LIBCXX_INSTALL_HEADERS))
+    add_custom_target(install-libcxx
+                      DEPENDS cxx
+                      COMMAND "${CMAKE_COMMAND}"
+                      -DCMAKE_INSTALL_COMPONENT=libcxx
+                      -P "${LIBCXX_BINARY_DIR}/cmake_install.cmake")
 endif()