lib: c: combine libc and ulibc

libc is now made up of several independent components, each of which is individually compiled into a static library.
they are then all combined into a single shared library.

lib/libc/core/string/strlen.c

@@ -0,0 +1,11 @@
+#include <string.h>
+
+size_t strlen(const char *str)
+{
+	size_t res = 0;
+	while (str[res]) {
+		res++;
+	}
+
+	return res;
+}