lib: c: re-organise into separate static modules, plus a single shared library

lib/libc/include/errno.h

@@ -139,4 +139,7 @@
 #define EQFULL          106 /* Interface output queue is full */
 #define ELAST           106 /* Must be equal largest errno */
 
+extern int __set_errno(int err);
+extern int __errno_from_kern_status(unsigned int err);
+
 #endif

lib/libc/include/string.h

@@ -14,4 +14,6 @@ extern int strncmp(const char *s1, const char *s2, unsigned long n);
 extern void *memset(void *str, int c, size_t n);
 extern void *memcpy(void *dst, const void *src, size_t len);
 
+extern char *strdup(char *s);
+
 #endif

lib/libc/include/unistd.h

@@ -1,9 +1,12 @@
 #ifndef UNISTD_H_
 #define UNISTD_H_
 
-#include <stdint.h>
+#include <stddef.h>
 
 extern int open(const char *path, int flags);
 extern int close(int fd);
 
+extern int read(int fd, void *buf, size_t count);
+extern int write(int fd, const void *buf, size_t count);
+
 #endif