commonlib/bsd: Add strcat() and strncat() functions

An upcoming vboot feature [1] will need strcat() to be defined in
string.h. Therefore, add strcat() and strncat() to commonlib/bsd. Remove
those functions from libpayload.

[1] https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5650810

Change-Id: If02fce0eafb4f6fa01d8bab17d87a32360f4ac83
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83765
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/libc/string.c

@@ -152,46 +152,6 @@ char *strcpy(char *d, const char *s)
 	return strncpy(d, s, strlen(s) + 1);
 }
 
-/**
- * Concatenates two strings
- *
- * @param d The destination string.
- * @param s The source string.
- * @return A pointer to the destination string.
- */
-char *strcat(char *d, const char *s)
-{
-	char *p = d + strlen(d);
-	size_t sl = strlen(s);
-
-	for (size_t i = 0; i < sl; i++)
-		p[i] = s[i];
-
-	p[sl] = '\0';
-	return d;
-}
-
-/**
- * Concatenates two strings with a maximum length.
- *
- * @param d The destination string.
- * @param s The source string.
- * @param n Not more than n characters from s will be appended to d.
- * @return A pointer to the destination string.
- */
-char *strncat(char *d, const char *s, size_t n)
-{
-	char *p = d + strlen(d);
-	size_t sl = strlen(s);
-	size_t max = n > sl ? sl : n;
-
-	for (size_t i = 0; i < max; i++)
-		p[i] = s[i];
-
-	p[max] = '\0';
-	return d;
-}
-
 /**
  * Concatenates two strings with a maximum length.
  *