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/memset.c

@@ -0,0 +1,13 @@
+#include <stddef.h>
+
+void *memset(void *str, int c, size_t n)
+{
+	unsigned char val = (unsigned char)c;
+	unsigned char *buf = str;
+
+	for (size_t i = 0; i < n; i++) {
+		buf[i] = val;
+	}
+
+	return str;
+}