There is no mallopt in musl.

--- src/gx_head/gui/machine.cpp.orig	2018-07-22 06:24:50.000000000 +0200
+++ src/gx_head/gui/machine.cpp	2018-08-26 09:31:01.815078037 +0200
@@ -44,8 +44,10 @@
     long int total_size = 0;
     if (mlockall(MCL_CURRENT | MCL_FUTURE))
         gx_print_error("system init", "mlockall failed:");
+#ifdef __GLIBC__
     mallopt(M_TRIM_THRESHOLD, -1);
     mallopt(M_MMAP_MAX, 0);
+#endif
     for (unsigned int i = 0; i < sizeof(regions)/sizeof(regions[0]); i++) {
         total_size +=regions[i].len;
         if (mlock(regions[i].start, regions[i].len) != 0) {
