With USE=-threads crystal crashes for me outright:
$ cat a.cr
puts hello
$ crystal build a.cr
Invalid memory access (signal 11) at address 0x0
[
12705341] __crystal_sigfault_handler +61
[
140316947557920] ???
[0] ???
Package-Manager: portage-2.3.0
# dev-libs/boehm-gc[static-libs] dependency problem, check the issue: https://github.com/manastech/crystal/issues/1382
DEPEND="
<sys-devel/llvm-3.7.0
- dev-libs/boehm-gc[static-libs]
+ dev-libs/boehm-gc[static-libs,threads]
dev-libs/libatomic_ops
dev-libs/libevent
dev-libs/libpcre
<email>longlene@gmail.com</email>
<name>Lixiao Chen</name>
</maintainer>
+ <maintainer type="person">
+ <email>slyfox@gentoo.org</email>
+ <name>Sergei Trofimovich</name>
+ </maintainer>
<maintainer type="project">
<email>proxy-maint@gentoo.org</email>
<name>Proxy Maintainers</name>