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

fusl/src/complex/casinhl.c

Index: fusl/src/complex/casinhl.c
diff --git a/fusl/src/complex/casinhl.c b/fusl/src/complex/casinhl.c
new file mode 100644
index 0000000000000000000000000000000000000000..714f189359071e31c9da7e52f66cb17df35facc9
--- /dev/null
+++ b/fusl/src/complex/casinhl.c
@@ -0,0 +1,14 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double complex casinhl(long double complex z)
+{
+	return casinh(z);
+}
+#else
+long double complex casinhl(long double complex z)
+{
+	z = casinl(CMPLXL(-cimagl(z), creall(z)));
+	return CMPLXL(cimagl(z), -creall(z));
+}
+#endif