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

fusl/src/stdlib/fcvt.c

Index: fusl/src/stdlib/fcvt.c
diff --git a/fusl/src/stdlib/fcvt.c b/fusl/src/stdlib/fcvt.c
new file mode 100644
index 0000000000000000000000000000000000000000..f90928fe160de88fa783d10bd0f10b44ac833950
--- /dev/null
+++ b/fusl/src/stdlib/fcvt.c
@@ -0,0 +1,25 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+char *fcvt(double x, int n, int *dp, int *sign)
+{
+	char tmp[1500];
+	int i, lz;
+
+	if (n > 1400U) n = 1400;
+	sprintf(tmp, "%.*f", n, x);
+	i = (tmp[0] == '-');
+	if (tmp[i] == '0') lz = strspn(tmp+i+2, "0");
+	else lz = -(int)strcspn(tmp+i, ".");
+
+	if (n<=lz) {
+		*sign = i;
+		*dp = 1;
+		if (n>14U) n = 14;
+		return "000000000000000"+14-n;
+	}
+
+	return ecvt(x, n-lz, dp, sign);
+}