[io.hpp] fix openAndWait and closeAndWait definitions

The posix versions (close/openat) return int as well.
And this fixes a narrowing conversion in c_emper.cpp: emper_openat and emper_close

emper/io.hpp

@@ -370,7 +370,7 @@ inline auto writevAndWait(int fildes, const struct iovec *iov, int iovcnt) -> ss
  *
  * @return fd on success, -1 on error
  */
-inline auto openatAndWait(int dirfd, const char *pathname, int flags, mode_t mode = 0) -> size_t {
+inline auto openatAndWait(int dirfd, const char *pathname, int flags, mode_t mode = 0) -> int {
 	OpenatFuture future(dirfd, pathname, flags, mode);
 	future.submit();
 	return future.waitAndSetErrno();
@@ -407,7 +407,7 @@ inline auto openatAndWait(int dirfd, const char *pathname, int flags, mode_t mod
  *
  * @return fd on success, -1 on error
  */
-inline auto openAndWait(const char *pathname, int flags, mode_t mode = 0) -> size_t {
+inline auto openAndWait(const char *pathname, int flags, mode_t mode = 0) -> int {
 	OpenatFuture future(AT_FDCWD, pathname, flags, mode);
 	future.submit();
 	return future.waitAndSetErrno();
@@ -439,7 +439,7 @@ inline auto openAndWait(const char *pathname, int flags, mode_t mode = 0) -> siz
  *
  * @return 0 on success, -1 on error
  */
-inline auto closeAndWait(int fd) -> ssize_t {
+inline auto closeAndWait(int fd) -> int {
 	CloseFuture future(fd);
 	future.submit();
 	return future.waitAndSetErrno();