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

fusl/src/math/__fpclassify.c

Index: fusl/src/math/__fpclassify.c
diff --git a/fusl/src/math/__fpclassify.c b/fusl/src/math/__fpclassify.c
new file mode 100644
index 0000000000000000000000000000000000000000..f7c0e2dfac828616b43f76664c6821de1b348f8d
--- /dev/null
+++ b/fusl/src/math/__fpclassify.c
@@ -0,0 +1,11 @@
+#include <math.h>
+#include <stdint.h>
+
+int __fpclassify(double x)
+{
+	union {double f; uint64_t i;} u = {x};
+	int e = u.i>>52 & 0x7ff;
+	if (!e) return u.i<<1 ? FP_SUBNORMAL : FP_ZERO;
+	if (e==0x7ff) return u.i<<12 ? FP_NAN : FP_INFINITE;
+	return FP_NORMAL;
+}