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
@@ -198,7 +198,6 @@
 check_symbol_exists(sysconf unistd.h HAVE_SYSCONF)
 check_symbol_exists(getrusage sys/resource.h HAVE_GETRUSAGE)
 check_symbol_exists(setrlimit sys/resource.h HAVE_SETRLIMIT)
-check_symbol_exists(isatty unistd.h HAVE_ISATTY)
 check_symbol_exists(futimens sys/stat.h HAVE_FUTIMENS)
 check_symbol_exists(futimes sys/time.h HAVE_FUTIMES)
 check_symbol_exists(posix_fallocate fcntl.h HAVE_POSIX_FALLOCATE)
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
@@ -88,9 +88,6 @@
 /* Define to 1 if you have the `getrusage' function. */
 #cmakedefine HAVE_GETRUSAGE ${HAVE_GETRUSAGE}
 
-/* Define to 1 if you have the `isatty' function. */
-#cmakedefine HAVE_ISATTY 1
-
 /* Define to 1 if you have the `edit' library (-ledit). */
 #cmakedefine HAVE_LIBEDIT ${HAVE_LIBEDIT}
 
diff --git a/llvm/lib/Support/Unix/Process.inc b/llvm/lib/Support/Unix/Process.inc
--- a/llvm/lib/Support/Unix/Process.inc
+++ b/llvm/lib/Support/Unix/Process.inc
@@ -272,12 +272,7 @@
 }
 
 bool Process::FileDescriptorIsDisplayed(int fd) {
-#if HAVE_ISATTY
   return isatty(fd);
-#else
-  // If we don't have isatty, just return false.
-  return false;
-#endif
 }
 
 static unsigned getColumns(int FileID) {
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
@@ -203,7 +203,6 @@
       "HAVE_GETPAGESIZE=",
       "HAVE_GETRLIMIT=",
       "HAVE_GETRUSAGE=",
-      "HAVE_ISATTY=",
       "HAVE_LIBPTHREAD=",
       "HAVE_PTHREAD_SETNAME_NP=",
       "HAVE_LIBZ=",
@@ -241,7 +240,6 @@
       "HAVE_GETPAGESIZE=1",
       "HAVE_GETRLIMIT=1",
       "HAVE_GETRUSAGE=1",
-      "HAVE_ISATTY=1",
       "HAVE_LIBPTHREAD=1",
       "HAVE_PTHREAD_SETNAME_NP=1",
       "HAVE_LIBZ=1",