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

fusl/src/string/memchr.c

+#include <string.h>
+#include <stdint.h>
+#include <limits.h>
+
+#define SS (sizeof(size_t))
+#define ALIGN (sizeof(size_t)-1)
+#define ONES ((size_t)-1/UCHAR_MAX)
+#define HIGHS (ONES * (UCHAR_MAX/2+1))
+#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
+
+void *memchr(const void *src, int c, size_t n)
+{
+        const unsigned char *s = src;
+        c = (unsigned char)c;
+        for (; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--);
+        if (n && *s != c) {
+                const size_t *w;
+                size_t k = ONES * c;
+                for (w = (const void *)s; n>=SS && !HASZERO(*w^k); w++, n-=SS);
+                for (s = (const void *)w; n && *s != c; s++, n--);
+        }
+        return n ? (void *)s : 0;
+}