Thanks for the patch Lain! See: https://bugs.gentoo.org/979033
diff --git a/configure.ac b/configure.ac
index 3ec2938..5fb9fef 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,7 +37,7 @@ AC_C_RESTRICT
 
 AC_CHECK_HEADERS([sys/ptrace.h sys/prctl.h])
 AC_CHECK_FUNCS([tcgetwinsize memmem strcasestr getline fseeko ftello])
-AC_CHECK_FUNCS([fpurge __fpurge strchrnul strndup gettid popen])
+AC_CHECK_FUNCS([__fpurge strchrnul strndup gettid popen])
 
 AC_CHECK_MEMBERS([struct stat.st_mtimespec.tv_nsec])
 AC_CHECK_MEMBERS([struct stat.st_mtim.tv_nsec])