diff --git a/flang/runtime/CMakeLists.txt b/flang/runtime/CMakeLists.txt
--- a/flang/runtime/CMakeLists.txt
+++ b/flang/runtime/CMakeLists.txt
@@ -50,7 +50,6 @@
 
 include(CheckCXXSymbolExists)
 include(CheckCXXSourceCompiles)
-check_cxx_symbol_exists(strerror string.h HAVE_STRERROR)
 check_cxx_symbol_exists(strerror_r string.h HAVE_STRERROR_R)
 # Can't use symbol exists here as the function is overloaded in C++
 check_cxx_source_compiles(
@@ -69,10 +68,6 @@
   set(NO_LTO_FLAGS "")
 endif()
 
-if (NOT (HAVE_STRERROR OR HAVE_STRERROR_R OR HAVE_DECL_STRERROR_S))
-  message(FATAL_ERROR "None of strerror, strerror_r, strerror_s found.")
-endif()
-
 configure_file(config.h.cmake config.h)
 # include_directories is used here instead of target_include_directories
 # because add_flang_library creates multiple objects (STATIC/SHARED, OBJECT)
diff --git a/flang/runtime/io-error.cpp b/flang/runtime/io-error.cpp
--- a/flang/runtime/io-error.cpp
+++ b/flang/runtime/io-error.cpp
@@ -122,14 +122,11 @@
 #endif
 #elif HAVE_DECL_STRERROR_S // "Windows Secure API"
   ok = ::strerror_s(buffer, bufferLength, ioStat_) == 0;
-#elif HAVE_STRERROR
+#else
   // Copy the thread un-safe result of strerror into
   // the buffer as fast as possible to minimize impact
   // of collision of strerror in multiple threads.
   msg = strerror(ioStat_);
-#else
-  // Strange that this system doesn't even have strerror
-  return false;
 #endif
   if (msg) {
     ToFortranDefaultCharacter(buffer, bufferLength, msg);
diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -299,7 +299,6 @@
 check_symbol_exists(posix_spawn spawn.h HAVE_POSIX_SPAWN)
 check_symbol_exists(pread unistd.h HAVE_PREAD)
 check_symbol_exists(sbrk unistd.h HAVE_SBRK)
-check_symbol_exists(strerror string.h HAVE_STRERROR)
 check_symbol_exists(strerror_r string.h HAVE_STRERROR_R)
 check_symbol_exists(strerror_s string.h HAVE_DECL_STRERROR_S)
 check_symbol_exists(setenv stdlib.h HAVE_SETENV)
diff --git a/llvm/include/llvm/Config/config.h.cmake b/llvm/include/llvm/Config/config.h.cmake
--- a/llvm/include/llvm/Config/config.h.cmake
+++ b/llvm/include/llvm/Config/config.h.cmake
@@ -176,9 +176,6 @@
 /* Define to 1 if you have the <signal.h> header file. */
 #cmakedefine HAVE_SIGNAL_H ${HAVE_SIGNAL_H}
 
-/* Define to 1 if you have the `strerror' function. */
-#cmakedefine HAVE_STRERROR ${HAVE_STRERROR}
-
 /* Define to 1 if you have the `strerror_r' function. */
 #cmakedefine HAVE_STRERROR_R ${HAVE_STRERROR_R}
 
diff --git a/llvm/lib/Support/Errno.cpp b/llvm/lib/Support/Errno.cpp
--- a/llvm/lib/Support/Errno.cpp
+++ b/llvm/lib/Support/Errno.cpp
@@ -55,17 +55,11 @@
 #elif HAVE_DECL_STRERROR_S // "Windows Secure API"
   strerror_s(buffer, MaxErrStrLen - 1, errnum);
   str = buffer;
-#elif defined(HAVE_STRERROR)
+#else
   // Copy the thread un-safe result of strerror into
   // the buffer as fast as possible to minimize impact
   // of collision of strerror in multiple threads.
   str = strerror(errnum);
-#else
-  // Strange that this system doesn't even have strerror
-  // but, oh well, just use a generic message
-  raw_string_ostream stream(str);
-  stream << "Error #" << errnum;
-  stream.flush();
 #endif
   return str;
 }
diff --git a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
--- a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
@@ -99,7 +99,6 @@
     "HAVE_LIBPSAPI=",
     "HAVE_MALLCTL=",
     "HAVE_SIGNAL_H=1",
-    "HAVE_STRERROR=1",
     "HAVE_SYS_STAT_H=1",
     "HAVE_SYS_TYPES_H=1",
     "HAVE_VALGRIND_VALGRIND_H=",
diff --git a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
--- a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
+++ b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
@@ -189,9 +189,6 @@
 /* Define to 1 if you have the <signal.h> header file. */
 #define HAVE_SIGNAL_H 1
 
-/* Define to 1 if you have the `strerror' function. */
-#define HAVE_STRERROR 1
-
 /* Define to 1 if you have the `strerror_r' function. */
 /* HAVE_STRERROR_R defined in Bazel */
 
diff --git a/utils/bazel/llvm_configs/config.h.cmake b/utils/bazel/llvm_configs/config.h.cmake
--- a/utils/bazel/llvm_configs/config.h.cmake
+++ b/utils/bazel/llvm_configs/config.h.cmake
@@ -176,9 +176,6 @@
 /* Define to 1 if you have the <signal.h> header file. */
 #cmakedefine HAVE_SIGNAL_H ${HAVE_SIGNAL_H}
 
-/* Define to 1 if you have the `strerror' function. */
-#cmakedefine HAVE_STRERROR ${HAVE_STRERROR}
-
 /* Define to 1 if you have the `strerror_r' function. */
 #cmakedefine HAVE_STRERROR_R ${HAVE_STRERROR_R}