Add a "fork" of musl as //fusl.

fusl/src/mman/mremap.c

Index: fusl/src/mman/mremap.c
diff --git a/fusl/src/mman/mremap.c b/fusl/src/mman/mremap.c
new file mode 100644
index 0000000000000000000000000000000000000000..ce4e8ea13677adc024dee57c21f810e6552c9c76
--- /dev/null
+++ b/fusl/src/mman/mremap.c
@@ -0,0 +1,33 @@
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include "syscall.h"
+#include "libc.h"
+
+static void dummy(void) { }
+weak_alias(dummy, __vm_wait);
+
+void *__mremap(void *old_addr, size_t old_len, size_t new_len, int flags, ...)
+{
+	va_list ap;
+	void *new_addr = 0;
+
+	if (new_len >= PTRDIFF_MAX) {
+		errno = ENOMEM;
+		return MAP_FAILED;
+	}
+
+	if (flags & MREMAP_FIXED) {
+		__vm_wait();
+		va_start(ap, flags);
+		new_addr = va_arg(ap, void *);
+		va_end(ap);
+	}
+
+	return (void *)syscall(SYS_mremap, old_addr, old_len, new_len, flags, new_addr);
+}
+
+weak_alias(__mremap, mremap);