Gentoo's Bugzilla –
Attachment 854950 Details for
Bug 898088net-misc/mptcpd-0.12 fails to compile (MUSL-CLANG-SYSTEM): network_monitor.c:50:19: error: call to undeclared function __bswap_constant_32; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]