tools/nolibc/string: add strncpy() and strlcpy()

These are minimal variants. strncpy() always fills the destination for
<size> chars, while strlcpy() copies no more than <size> including the
zero and returns the source's length. The respective sizes on various
archs are:

  strncpy(): x86:0x1f mips:0x30 arm:0x20
  strlcpy(): x86:0x17 mips:0x34 arm:0x1a
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/string.h

@@ -121,6 +121,34 @@ size_t nolibc_strlen(const char *str)
 		nolibc_strlen((str));           \
 })
 
+static __attribute__((unused))
+size_t strlcpy(char *dst, const char *src, size_t size)
+{
+	size_t len;
+	char c;
+
+	for (len = 0;;) {
+		c = src[len];
+		if (len < size)
+			dst[len] = c;
+		if (!c)
+			break;
+		len++;
+	}
+	return len;
+}
+
+static __attribute__((unused))
+char *strncpy(char *dst, const char *src, size_t size)
+{
+	size_t len;
+
+	for (len = 0; len < size; len++)
+		if ((dst[len] = *src))
+			src++;
+	return dst;
+}
+
 static __attribute__((unused))
 char *strrchr(const char *s, int c)
 {