diff --git a/icu4c/source/aclocal.m4 b/icu4c/source/aclocal.m4
index 1e0201d1e27f..4c8464d28826 100644
--- a/icu4c/source/aclocal.m4
+++ b/icu4c/source/aclocal.m4
@@ -12,60 +12,6 @@
 # PARTICULAR PURPOSE.
 
 m4_ifndef([AC_CONFIG_MACRO_DIRS], [m4_defun([_AM_CONFIG_MACRO_DIRS], [])m4_defun([AC_CONFIG_MACRO_DIRS], [_AM_CONFIG_MACRO_DIRS($@)])])
-# ===========================================================================
-#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
-# ===========================================================================
-#
-# SYNOPSIS
-#
-#   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
-#
-# DESCRIPTION
-#
-#   Check whether the given FLAG works with the current language's compiler
-#   or gives an error.  (Warnings, however, are ignored)
-#
-#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
-#   success/failure.
-#
-#   If EXTRA-FLAGS is defined, it is added to the current language's default
-#   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
-#   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
-#   force the compiler to issue an error when a bad flag is given.
-#
-#   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
-#
-#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
-#   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
-#
-# LICENSE
-#
-#   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
-#   Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
-#
-#   Copying and distribution of this file, with or without modification, are
-#   permitted in any medium without royalty provided the copyright notice
-#   and this notice are preserved.  This file is offered as-is, without any
-#   warranty.
-
-#serial 6
-
-AC_DEFUN([AX_CHECK_COMPILE_FLAG],
-[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
-AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
-AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
-  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
-  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
-  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
-    [AS_VAR_SET(CACHEVAR,[yes])],
-    [AS_VAR_SET(CACHEVAR,[no])])
-  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
-AS_VAR_IF(CACHEVAR,yes,
-  [m4_default([$2], :)],
-  [m4_default([$3], :)])
-AS_VAR_POPDEF([CACHEVAR])dnl
-])dnl AX_CHECK_COMPILE_FLAGS
-
 dnl pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
 dnl serial 11 (pkg-config-0.29.1)
 dnl
diff --git a/icu4c/source/configure b/icu4c/source/configure
index d2ee1acecdd2..db50f3470a1b 100755
--- a/icu4c/source/configure
+++ b/icu4c/source/configure
@@ -4264,8 +4264,6 @@ fi
 #AC_CHECK_PROG(AUTOCONF, autoconf, autoconf, true)
 #AC_CHECK_PROG(STRIP, strip, strip, true)
 
-
-
 # TODO(ICU-20301): Remove fallback to Python 2.
 for ac_prog in python3 "py -3" python "py"
 do
@@ -7980,56 +7978,6 @@ fi
 # Now that we're done using CPPFLAGS etc. for tests, we can change it
 # for build.
 
-ac_ext=cpp
-ac_cpp='$CXXCPP $CPPFLAGS'
-ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
-ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
-ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
-
-# Silence a Clang warning about ambiguous operators with C++20 rewritten
-# expressions that possibly or maybe even probably is a mistake (ICU-20973).
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -Wambiguous-reversed-operator" >&5
-$as_echo_n "checking whether C++ compiler accepts -Wambiguous-reversed-operator... " >&6; }
-if ${ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-
-  ax_check_save_flags=$CXXFLAGS
-  CXXFLAGS="$CXXFLAGS -Werror -Wambiguous-reversed-operator"
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_cxx_try_compile "$LINENO"; then :
-  ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator=yes
-else
-  ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator=no
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-  CXXFLAGS=$ax_check_save_flags
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator" >&5
-$as_echo "$ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator" >&6; }
-if test "x$ax_cv_check_cxxflags__Werror__Wambiguous_reversed_operator" = xyes; then :
-  CXXFLAGS+=" -Wno-ambiguous-reversed-operator"
-else
-  :
-fi
-
-ac_ext=c
-ac_cpp='$CPP $CPPFLAGS'
-ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
-ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
-ac_compiler_gnu=$ac_cv_c_compiler_gnu
-
-
 if test "${CC}" = "clang"; then
    CLANGCFLAGS="-Qunused-arguments -Wno-parentheses-equality"
 else