Index: compiler-rt/cmake/config-ix.cmake
===================================================================
--- compiler-rt/cmake/config-ix.cmake
+++ compiler-rt/cmake/config-ix.cmake
@@ -12,7 +12,7 @@
   cmake_pop_check_state()
 endfunction()
 
-check_library_exists(c fopen "" COMPILER_RT_HAS_LIBC)
+check_library_exists(c atexit "" COMPILER_RT_HAS_LIBC)
 if (COMPILER_RT_USE_BUILTINS_LIBRARY)
   include(HandleCompilerRT)
   find_compiler_rt_library(builtins COMPILER_RT_BUILTINS_LIBRARY)
Index: libcxx/cmake/config-ix.cmake
===================================================================
--- libcxx/cmake/config-ix.cmake
+++ libcxx/cmake/config-ix.cmake
@@ -7,7 +7,7 @@
   # let the default linking take care of that.
   set(LIBCXX_HAS_C_LIB NO)
 else()
-  check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)
+  check_library_exists(c atexit "" LIBCXX_HAS_C_LIB)
 endif()
 
 if (NOT LIBCXX_USE_COMPILER_RT)
Index: libcxxabi/cmake/config-ix.cmake
===================================================================
--- libcxxabi/cmake/config-ix.cmake
+++ libcxxabi/cmake/config-ix.cmake
@@ -2,7 +2,7 @@
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
-check_library_exists(c fopen "" LIBCXXABI_HAS_C_LIB)
+check_library_exists(c atexit "" LIBCXXABI_HAS_C_LIB)
 if (NOT LIBCXXABI_USE_COMPILER_RT)
   check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_S_LIB)
 endif ()
Index: libunwind/cmake/config-ix.cmake
===================================================================
--- libunwind/cmake/config-ix.cmake
+++ libunwind/cmake/config-ix.cmake
@@ -3,7 +3,7 @@
 include(CheckCXXCompilerFlag)
 include(CheckLibraryExists)
 
-check_library_exists(c fopen "" LIBUNWIND_HAS_C_LIB)
+check_library_exists(c atexit "" LIBUNWIND_HAS_C_LIB)
 
 if (NOT LIBUNWIND_USE_COMPILER_RT)
   check_library_exists(gcc_s __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_S_LIB)
Index: llvm/runtimes/CMakeLists.txt
===================================================================
--- llvm/runtimes/CMakeLists.txt
+++ llvm/runtimes/CMakeLists.txt
@@ -98,7 +98,7 @@
   include(CheckLibraryExists)
   include(CheckCCompilerFlag)
 
-  check_library_exists(c fopen "" LLVM_HAS_C_LIB)
+  check_library_exists(c atexit "" LLVM_HAS_C_LIB)
   check_c_compiler_flag(-nodefaultlibs LLVM_HAS_NODEFAULTLIBS_FLAG)
   if(LLVM_HAS_NODEFAULTLIBS_FLAG)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")