[GOLD] gcc-11 stringop-overflow warning

[GOLD] gcc-11 stringop-overflow warning

I'm unsure why this is deserving of a warning.  Not writing the most
efficient code surely can't be a real problem, but that is what
https://gcc.gnu.org/bugzilla//show_bug.cgi?id=88059#c1 seems to say.

plugin.cc:528:10: error: 'char* strncpy(char*, const char*, size_t)' specified bound depends on the length of the source argument [-Werror=stringop-overflow=]
  528 |   strncpy(tempdir, dir_template, len);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
plugin.cc:526:22: note: length computed here
  526 |   size_t len = strlen(dir_template) + 1;
      |                ~~~~~~^~~~~~~~~~~~~~

	* plugin.cc (Plugin_recorder::init): Replace strncpy with memcpy.