From dc1b8ca26ec88f392f61927b287dce00d4880d6e Mon Sep 17 00:00:00 2001
From: Fredrik Roubert <roubert@google.com>
Date: Wed, 4 Aug 2021 17:27:52 +0200
Subject: [PATCH] ICU-20973 Use the Clang -Wno-ambiguous-reversed-operator
 flag.

---
 icu4c/source/configure.ac | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/icu4c/source/configure.ac b/icu4c/source/configure.ac
index 2331ac1ef6c..525dd126e9f 100644
--- a/icu4c/source/configure.ac
+++ b/icu4c/source/configure.ac
@@ -1317,6 +1317,16 @@ fi
 # Now that we're done using CPPFLAGS etc. for tests, we can change it
 # for build.
 
+AC_LANG_PUSH([C++])
+# Silence a Clang warning about ambiguous operators with C++20 rewritten
+# expressions that possibly or maybe even probably is a mistake (ICU-20973).
+AX_CHECK_COMPILE_FLAG(
+  [-Wambiguous-reversed-operator],
+  [CXXFLAGS+=" -Wno-ambiguous-reversed-operator"],
+  [],
+  [-Werror])
+AC_LANG_POP([C++])
+
 if test "${CC}" = "clang"; then
    CLANGCFLAGS="-Qunused-arguments -Wno-parentheses-equality"
 else