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

fusl/src/complex/cacosl.c

Index: fusl/src/complex/cacosl.c
diff --git a/fusl/src/complex/cacosl.c b/fusl/src/complex/cacosl.c
new file mode 100644
index 0000000000000000000000000000000000000000..7fd4a2f6b442404b00e9ea133e0e6e90dec8b057
--- /dev/null
+++ b/fusl/src/complex/cacosl.c
@@ -0,0 +1,16 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double complex cacosl(long double complex z)
+{
+	return cacos(z);
+}
+#else
+// FIXME
+#define PI_2 1.57079632679489661923132169163975144L
+long double complex cacosl(long double complex z)
+{
+	z = casinl(z);
+	return CMPLXL(PI_2 - creall(z), -cimagl(z));
+}
+#endif