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

fusl/src/internal/shgetc.c

Index: fusl/src/internal/shgetc.c
diff --git a/fusl/src/internal/shgetc.c b/fusl/src/internal/shgetc.c
new file mode 100644
index 0000000000000000000000000000000000000000..e878b00ad50ac709b33366f11619817c1e535636
--- /dev/null
+++ b/fusl/src/internal/shgetc.c
@@ -0,0 +1,27 @@
+#include "shgetc.h"
+
+void __shlim(FILE *f, off_t lim)
+{
+	f->shlim = lim;
+	f->shcnt = f->rend - f->rpos;
+	if (lim && f->shcnt > lim)
+		f->shend = f->rpos + lim;
+	else
+		f->shend = f->rend;
+}
+
+int __shgetc(FILE *f)
+{
+	int c;
+	if (f->shlim && f->shcnt >= f->shlim || (c=__uflow(f)) < 0) {
+		f->shend = 0;
+		return EOF;
+	}
+	if (f->shlim && f->rend - f->rpos > f->shlim - f->shcnt - 1)
+		f->shend = f->rpos + (f->shlim - f->shcnt - 1);
+	else
+		f->shend = f->rend;
+	if (f->rend) f->shcnt += f->rend - f->rpos + 1;
+	if (f->rpos[-1] != c) f->rpos[-1] = c;
+	return c;
+}