PharFileInfo::chmod() allows setting of the executable
file permissions bit, as well as read-only bits. Writeable bits are
ignored, and set at runtime based on the
phar.readonly INI variable.
As with all functionality that modifies the contents of
a phar, the phar.readonly INI variable
must be off in order to succeed if the file is within a Phar
archive. Files within PharData archives do not have
this restriction.