https://bugs.gentoo.org/767706
https://gcc.gnu.org/PR99172

From c2be82058fb40f3ae891c68d185ff53e07f14f45 Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice@google.com>
Date: Fri, 12 Mar 2021 07:34:36 -0800
Subject: [PATCH] libstdc++-v3: Update VTV vars for libtool link commands
 [PR99172]

This fixes PR 99172

Currently when GCC is configured with --enable-vtable-verify, the
libstdc++-v3 Makefiles add "-fvtable-verify=std
-Wl,-u_vtable_map_vars_start,-u_vtable_map_vars_end" to libtool link
commands. The "-fvtable-verify=std" piece causes alternate versions of
libtool (such as slibtool) to fail, unable to find "-lvtv" (GNU
libtool just removes that piece).

This patch updates the libstdc++-v3 Makefiles to not pass
"-fvtable-verify=std" to the libtool link commands.
---
 libstdc++-v3/src/Makefile.am | 4 +++-
 libstdc++-v3/src/Makefile.in | 3 ++-

--- a/libstdc++-v3/src/Makefile.am
+++ b/libstdc++-v3/src/Makefile.am
@@ -214,12 +214,14 @@ compatibility-condvar.o: compatibility-condvar.cc
 # set this option because CONFIG_CXXFLAGS has to be after
 # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
 # as the occasion calls for it.
-AM_CXXFLAGS = \
+AM_CXXFLAGS_PRE = \
 	-std=gnu++98 \
 	$(glibcxx_compiler_pic_flag) \
 	$(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
 	$(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS)
 
+AM_CXXFLAGS = $(filter-out -fvtable-verify=std,$(AM_CXXFLAGS_PRE))
+
 # Libtool notes
 
 # 1) In general, libtool expects an argument such as `--tag=CXX' when
--- a/libstdc++-v3/src/Makefile.in
+++ b/libstdc++-v3/src/Makefile.in
@@ -578,12 +578,13 @@ libstdc___la_LINK = $(CXXLINK) $(libstdc___la_LDFLAGS) $(lt_host_flags)
 # set this option because CONFIG_CXXFLAGS has to be after
 # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
 # as the occasion calls for it.
-AM_CXXFLAGS = \
+AM_CXXFLAGS_PRE = \
 	-std=gnu++98 \
 	$(glibcxx_compiler_pic_flag) \
 	$(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
 	$(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS)
 
+AM_CXXFLAGS = $(filter-out -fvtable-verify=std,$(AM_CXXFLAGS_PRE))
 
 # Libtool notes
 
-- 
2.30.2