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

fusl/arch/aarch64/bits/fenv.h

Index: fusl/arch/aarch64/bits/fenv.h
diff --git a/fusl/arch/aarch64/bits/fenv.h b/fusl/arch/aarch64/bits/fenv.h
new file mode 100644
index 0000000000000000000000000000000000000000..2f3279abcf0eb73c21f76dcca791da9ccb7a75ec
--- /dev/null
+++ b/fusl/arch/aarch64/bits/fenv.h
@@ -0,0 +1,19 @@
+#define FE_INVALID    1
+#define FE_DIVBYZERO  2
+#define FE_OVERFLOW   4
+#define FE_UNDERFLOW  8
+#define FE_INEXACT    16
+#define FE_ALL_EXCEPT 31
+#define FE_TONEAREST  0
+#define FE_DOWNWARD   0x800000
+#define FE_UPWARD     0x400000
+#define FE_TOWARDZERO 0xc00000
+
+typedef unsigned int fexcept_t;
+
+typedef struct {
+	unsigned int __fpcr;
+	unsigned int __fpsr;
+} fenv_t;
+
+#define FE_DFL_ENV      ((const fenv_t *) -1)