dev-qt/qtwebengine: workaround -D_GLIBCXX_ASSERTIONS issues in 6.8

...which is default on hardened profiles, and unfortunately cannot
revbump only for hardened, so will cause unnecessary rebuilds.

Ideally would backport the proper fix, but have not tried to identify
what fixes this and, given workaround is temporary (should be fixed in
6.9), it may not be worth the trouble meanwhile.

On a side-note, was able to reproduce with qutebrowser by visiting some
specific websites.

Closes: https://bugs.gentoo.org/947356
Signed-off-by: Ionen Wolkens <ionen@gentoo.org>

dev-qt/qtwebengine/qtwebengine-6.8.1-r1.ebuild

@@ -1,4 +1,4 @@
-# Copyright 2021-2024 Gentoo Authors
+# Copyright 2021-2025 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
@@ -236,6 +236,9 @@ src_configure() {
 	if use !custom-cflags; then
 		strip-flags # fragile
 
+		# temporary workaround for bug #947356, should be fixed in Qt 6.9.x
+		append-cppflags -U_GLIBCXX_ASSERTIONS
+
 		if is-flagq '-g?(gdb)?([2-9])'; then #914475
 			replace-flags '-g?(gdb)?([2-9])' -g1
 			ewarn "-g2+/-ggdb* *FLAGS replaced with -g1 (enable USE=custom-cflags to keep)"

dev-qt/qtwebengine/qtwebengine-6.8.9999.ebuild

@@ -1,4 +1,4 @@
-# Copyright 2021-2024 Gentoo Authors
+# Copyright 2021-2025 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
@@ -235,6 +235,9 @@ src_configure() {
 	if use !custom-cflags; then
 		strip-flags # fragile
 
+		# temporary workaround for bug #947356, should be fixed in Qt 6.9.x
+		append-cppflags -U_GLIBCXX_ASSERTIONS
+
 		if is-flagq '-g?(gdb)?([2-9])'; then #914475
 			replace-flags '-g?(gdb)?([2-9])' -g1
 			ewarn "-g2+/-ggdb* *FLAGS replaced with -g1 (enable USE=custom-cflags to keep)"