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

fusl/src/internal/shgetc.h

Index: fusl/src/internal/shgetc.h
diff --git a/fusl/src/internal/shgetc.h b/fusl/src/internal/shgetc.h
new file mode 100644
index 0000000000000000000000000000000000000000..7beb8ce62182b64bb6f7349640b6f2d833b113c3
--- /dev/null
+++ b/fusl/src/internal/shgetc.h
@@ -0,0 +1,9 @@
+#include "stdio_impl.h"
+
+void __shlim(FILE *, off_t);
+int __shgetc(FILE *);
+
+#define shcnt(f) ((f)->shcnt + ((f)->rpos - (f)->rend))
+#define shlim(f, lim) __shlim((f), (lim))
+#define shgetc(f) (((f)->rpos < (f)->shend) ? *(f)->rpos++ : __shgetc(f))
+#define shunget(f) ((f)->shend ? (void)(f)->rpos-- : (void)0)