LYR-RES0013
a single file named std.lyr
A file built by itself, outside a package, is named std.lyr: its module would be named std.
Explanation
A single file is a package of its own, named after the file. std is the standard library's name, and a file of that name would claim it; a package's manifest refuses the name the same way.
Rename the file.
Example
$ lyric5 build std.lyr
error[LYR-RES0013]: 'std' is the standard library's name — a single file named std.lyr would claim it; rename the file
--> std.lyr:1:1