libc cleanup (#1568)

* libc cleanup

* Suggested changes, small alloca tweak

* Remove printf include

include/libc/string.h

@@ -0,0 +1,11 @@
+#ifndef STRING_H
+#define STRING_H
+
+#include "stddef.h"
+
+char* strchr(const char*, int);
+size_t strlen(const char*);
+
+void* memcpy(void*, const void*, size_t);
+
+#endif