When xhpast version is out of date and I'm running `arc lint`, then this is what `ArcanistPhutilXHPASTLinter` outputs:
```
Exception
Some linters failed:
- ArcanistPhutilXHPASTLinter: PhutilProxyException: Your version of 'xhpast' is unbuilt or out of date. Run this script to build it:
$ /usr/local/phabricator/libphutil/scripts/build_xhpast.php
- ArcanistXHPASTLinter: PhutilProxyException: Your version of 'xhpast' is unbuilt or out of date. Run this script to build it:
$ /usr/local/phabricator/libphutil/scripts/build_xhpast.php
- ArcanistPhutilLibraryLinter: CommandException: Command failed with error #2!
COMMAND
'gmake' -C '/usr/local/phabricator/libphutil/support/xhpast' 'clean' 'all' 'install'
STDOUT
gmake: Entering directory `/usr/local/phabricator/libphutil/support/xhpast'
rm xhpast parser.yacc.output libxhpast.a *.o 2>/dev/null
g++ -c -fPIC -g -Wall -O3 -minline-all-stringops -o scanner.lex.o scanner.lex.cpp
gmake: Leaving directory `/usr/local/phabricator/libphutil/support/xhpast'
STDERR
gmake: [clean] Error 1 (ignored)
scanner.lex.cpp: In function ‘yy_state_type yy_try_NUL_trans(yy_state_type, void*)’:
scanner.lex.cpp:5227:23: warning: unused variable ‘yyg’
Assembler messages:
Fatal error: can't create scanner.lex.o: Permission denied
gmake: *** [scanner.lex.o] Error 1
(Run with `--trace` for a full exception trace.)
```
Problem is, that file referenced `/usr/local/phabricator/libphutil/scripts/build_xhpast.php` doesn't exist. I only have `/usr/local/phabricator/libphutil/scripts/build_xhpast.sh` (the `sh` file extension instead of `php` file extension).