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

fusl/src/string/strspn.c

Index: fusl/src/string/strspn.c
diff --git a/fusl/src/string/strspn.c b/fusl/src/string/strspn.c
new file mode 100644
index 0000000000000000000000000000000000000000..9543dad09a3aba8bf2c616fb00d492f0e9fb94cd
--- /dev/null
+++ b/fusl/src/string/strspn.c
@@ -0,0 +1,20 @@
+#include <string.h>
+
+#define BITOP(a,b,op) \
+ ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
+
+size_t strspn(const char *s, const char *c)
+{
+	const char *a = s;
+	size_t byteset[32/sizeof(size_t)] = { 0 };
+
+	if (!c[0]) return 0;
+	if (!c[1]) {
+		for (; *s == *c; s++);
+		return s-a;
+	}
+
+	for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
+	for (; *s && BITOP(byteset, *(unsigned char *)s, &); s++);
+	return s-a;
+}