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

fusl/src/complex/cacos.c

Index: fusl/src/complex/cacos.c
diff --git a/fusl/src/complex/cacos.c b/fusl/src/complex/cacos.c
new file mode 100644
index 0000000000000000000000000000000000000000..27c356364c8c6ffe438767352195e791ed03a23f
--- /dev/null
+++ b/fusl/src/complex/cacos.c
@@ -0,0 +1,11 @@
+#include "libm.h"
+
+// FIXME: Hull et al. "Implementing the complex arcsine and arccosine functions using exception handling" 1997
+
+/* acos(z) = pi/2 - asin(z) */
+
+double complex cacos(double complex z)
+{
+	z = casin(z);
+	return CMPLX(M_PI_2 - creal(z), -cimag(z));
+}