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/include/unistd.h

@@ -0,0 +1,9 @@
+#ifndef UNISTD_H_
+#define UNISTD_H_
+
+#include <stdint.h>
+
+extern int open(const char *path, int flags);
+extern int close(int fd);
+
+#endif