Gentoo's Bugzilla –
Attachment 851940 Details for
Bug 895028dev-lang/srf-1.0-r2 fails to compile (MUSL-CLANG-SYSTEM): rfunc.c:54:2: error: call to undeclared library function exit with type void (int) __attribute__((noreturn)); ISO C99 and later do not support implicit function declarations [-Wimplicit-function-d