Fix missing errno assignments.

In PR #294 I removed a little too much code; we still need to assign to
`errno` in the code in question here.

Author: sunfishcode

libc-bottom-half/cloudlibc/src/libc/dirent/fdopendir.c

@@ -29,6 +29,7 @@ DIR *fdopendir(int fd) {
   if (error != 0) {
     free(dirp->buffer);
     free(dirp);
+    errno = error;
     return NULL;
   }
 

libc-bottom-half/cloudlibc/src/libc/fcntl/openat.c

@@ -73,6 +73,7 @@ int __wasilibc_nocwd_openat_nomode(int fd, const char *path, int oflag) {
                                  fs_rights_base, fs_rights_inheriting, fs_flags,
                                  &newfd);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return newfd;

libc-bottom-half/cloudlibc/src/libc/stdio/renameat.c

@@ -10,6 +10,7 @@
 int __wasilibc_nocwd_renameat(int oldfd, const char *old, int newfd, const char *new) {
   __wasi_errno_t error = __wasi_path_rename(oldfd, old, newfd, new);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return 0;

libc-bottom-half/cloudlibc/src/libc/sys/socket/recv.c

@@ -33,6 +33,7 @@ ssize_t recv(int socket, void *restrict buffer, size_t length, int flags) {
                                           &ro_datalen,
                                           &ro_flags);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return ro_datalen;

libc-bottom-half/cloudlibc/src/libc/sys/socket/send.c

@@ -25,6 +25,7 @@ ssize_t send(int socket, const void *buffer, size_t length, int flags) {
   size_t so_datalen;
   __wasi_errno_t error = __wasi_sock_send(socket, si_data, si_data_len, si_flags, &so_datalen);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return so_datalen;

libc-bottom-half/cloudlibc/src/libc/sys/socket/shutdown.c

@@ -20,6 +20,7 @@ int shutdown(int socket, int how) {
 
   __wasi_errno_t error = __wasi_sock_shutdown(socket, how);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return error;

libc-bottom-half/cloudlibc/src/libc/sys/stat/fstatat.c

@@ -23,6 +23,7 @@ int __wasilibc_nocwd_fstatat(int fd, const char *restrict path, struct stat *res
   __wasi_errno_t error =
       __wasi_path_filestat_get(fd, lookup_flags, path, &internal_stat);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   to_public_stat(&internal_stat, buf);

libc-bottom-half/cloudlibc/src/libc/sys/stat/mkdirat.c

@@ -11,6 +11,7 @@
 int __wasilibc_nocwd_mkdirat_nomode(int fd, const char *path) {
   __wasi_errno_t error = __wasi_path_create_directory(fd, path);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return 0;

libc-bottom-half/cloudlibc/src/libc/sys/stat/utimensat.c

@@ -18,6 +18,7 @@ int __wasilibc_nocwd_utimensat(int fd, const char *path, const struct timespec t
   __wasi_timestamp_t st_mtim;
   __wasi_fstflags_t flags;
   if (!utimens_get_timestamps(times, &st_atim, &st_mtim, &flags)) {
+    errno = EINVAL;
     return -1;
   }
 
@@ -30,6 +31,7 @@ int __wasilibc_nocwd_utimensat(int fd, const char *path, const struct timespec t
   __wasi_errno_t error =
       __wasi_path_filestat_set_times(fd, lookup_flags, path, st_atim, st_mtim, flags);
   if (error != 0) {
+    errno = error;
     return -1;
   }
   return 0;

libc-bottom-half/cloudlibc/src/libc/unistd/faccessat.c

@@ -22,6 +22,7 @@ int __wasilibc_nocwd_faccessat(int fd, const char *path, int amode, int flag) {
   __wasi_errno_t error =
       __wasi_path_filestat_get(fd, lookup_flags, path, &file);
   if (error != 0) {
+    errno = error;
     return -1;
   }