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>

src/commonlib/bsd/include/commonlib/bsd/string.h

@@ -8,6 +8,8 @@
 
 size_t strlen(const char *src);
 size_t strnlen(const char *str, size_t maxlen);
+char *strcat(char *dst, const char *src);
+char *strncat(char *dst, const char *src, size_t n);
 
 unsigned int skip_atoi(char **ptr);
 

src/commonlib/bsd/string.c

@@ -23,6 +23,29 @@ size_t strnlen(const char *str, size_t maxlen)
 	return ptr - str - 1;
 }
 
+char *strcat(char *dst, const char *src)
+{
+	char *ptr = dst + strlen(dst);
+
+	while (*src)
+		*ptr++ = *src++;
+
+	*ptr = '\0';
+	return dst;
+}
+
+char *strncat(char *dst, const char *src, size_t n)
+{
+	char *ptr = dst + strlen(dst);
+
+	/* Not using strncpy() because '\0' may not be appended. */
+	while (n-- > 0 && *src)
+		*ptr++ = *src++;
+
+	*ptr = '\0';
+	return dst;
+}
+
 unsigned int skip_atoi(char **ptr)
 {
 	unsigned int result = 0;