From 92bb096468f98c16ae903d48585ac57d5938771f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Tue, 10 Nov 2020 23:49:21 +0200
Subject: [PATCH] build-libcxx: Avoid warnings when building latest libcxxabi

---
 build-libcxx.sh | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/build-libcxx.sh b/build-libcxx.sh
index 0308044..304dec5 100755
--- a/build-libcxx.sh
+++ b/build-libcxx.sh
@@ -184,7 +184,14 @@ build_all() {
         mkdir -p build-$arch-$type
         cd build-$arch-$type
         if [ "$type" = "shared" ]; then
-            LIBCXXABI_VISIBILITY_FLAGS="-D_LIBCPP_BUILDING_LIBRARY= -U_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS"
+            # Define _LIBCPP_BUILDING_LIBRARY, to an empty string to match
+            # cases in source files that also do
+            # "#define _LIBCPP_BUILDING_LIBRARY". Since Nov 3 2020, libcxxabi
+            # itself also defines this, but with a plain
+            # -D_LIBCPP_BUILDING_LIBRARY, which defines it to 1. Therefore,
+            # first undefine any potential existing define from the command
+            # line, to avoid conflicts.
+            LIBCXXABI_VISIBILITY_FLAGS="-U_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_BUILDING_LIBRARY= -U_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS"
         else
             LIBCXXABI_VISIBILITY_FLAGS=""
         fi