Add strcasestr()

We'll need it for the next commit, if the platform does not
provide it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/lib/strcasestr.h b/lib/strcasestr.h
new file mode 100644
index 0000000..43d61df
--- /dev/null
+++ b/lib/strcasestr.h
@@ -0,0 +1,13 @@
+#ifdef CONFIG_STRCASESTR
+
+#include <string.h>
+
+#else
+
+#ifndef FIO_STRCASESTR_H
+#define FIO_STRCASESTR_H
+
+char *strcasestr(const char *haystack, const char *needle);
+
+#endif
+#endif