Add strstr implementation

Implement custom strstr function.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: Id5998fb9c3797f9a35aa40aedbd8cac8d56cf895
diff --git a/components/common/libc/src/strstr.c b/components/common/libc/src/strstr.c
new file mode 100644
index 0000000..0192d0f
--- /dev/null
+++ b/components/common/libc/src/strstr.c
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2024, Arm Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stddef.h>
+#include <string.h>
+
+char *strstr(const char *haystack, const char *needle)
+{
+	const char *h = NULL;
+	size_t needle_len = 0;
+
+	if (needle[0] == '\0')
+		return (char *)haystack;
+
+	needle_len = strlen(needle);
+	for (h = haystack; (h = strchr(h, needle[0])) != 0; h++)
+		if (strncmp(h, needle, needle_len) == 0)
+			return (char *)h;
+
+	return NULL;
+}