First of all - the neon useflag is intended for arm and masked on all other arches. The code behind it looks like this: # Modifications to better support ARM, bug 553364 if use neon ; then mozconfig_annotate '' --with-fpu=neon mozconfig_annotate '' --with-thumb=yes mozconfig_annotate '' --with-thumb-interwork=no fi At least one of the flags is rejected by clang, propably those related to thumb, as clang doesn't seem to support it. I'll hand in a proper build.log later on, my arm device is busy with other tasks at the moment. So this bug is a reminder to myself for the most of it. Please don't hardmask the clang useflag or remove tc-is-clang for arm profiles, because even if there is no official support for clang in Gentoo for arm profiles, firefox compiled by gcc on arm leads to a segfault at startup for the firefox binary, rendering the use of tc-is-gcc on arm as a waste of time. possible solution: make them conflict with each other, so that USE="clang neon" emerge -av =firefox-62.0.2 would blow up before portage starts emerging. It wouldn't affect any other arches, as the neon useflag is masked on those.
The bug has been referenced in the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=2d25811f80b28d70558fdfff1391a856fbffd47f commit 2d25811f80b28d70558fdfff1391a856fbffd47f Author: Thomas Deutschmann <whissi@gentoo.org> AuthorDate: 2018-09-27 14:30:48 +0000 Commit: Thomas Deutschmann <whissi@gentoo.org> CommitDate: 2018-09-27 14:30:48 +0000 www-client/firefox: clang doesn't support thumb-interwork Bug: https://bugs.gentoo.org/666966 Signed-off-by: Thomas Deutschmann <whissi@gentoo.org> Package-Manager: Portage-2.3.50, Repoman-2.3.11 www-client/firefox/firefox-62.0.2.ebuild | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
Case closed, thanks for the fast fix!