This is an auto-filled bug because dev-libs/libbulletml calls g++ directly.
The issue was originally discovered on amd64, but it may be reproducible on other arches as well.
If you think that a different summary clarifies the issue better, feel free to change it.
Attached build log and emerge --info.
If you think it doesn't make sense fix these type of issues, I'd like to point out that won't be possible use a different CXX implementation (like clang++) by setting the CXX variable. So this issue has been reproduced by setting the CXX variable to x86_64-pc-linux-gnu-g++ and by removing the /usr/bin/g++ - /usr/bin/c++ binaries.
Created attachment 639006 [details]
build log and emerge --info
The bug has been closed via the following commit(s):
Author: David Seifert <firstname.lastname@example.org>
AuthorDate: 2020-07-05 00:23:15 +0000
Commit: David Seifert <email@example.com>
CommitDate: 2020-07-05 00:23:15 +0000
dev-libs/libbulletml: Pass AR/CXX to build system
Package-Manager: Portage-2.3.103, Repoman-2.3.23
Signed-off-by: David Seifert <firstname.lastname@example.org>
.../files/libbulletml-0.0.6-Makefile.patch | 119 +++++++++++++++++++++
dev-libs/libbulletml/libbulletml-0.0.6.ebuild | 17 +--
2 files changed, 128 insertions(+), 8 deletions(-)