gprofng: Use execvp instead of execv

gp-display-gui (https://savannah.gnu.org/projects/gprofng-gui)
can be installed in a different directory.
In this case, $PATH is used to look up gp-display-text.
execv() does not use $PATH to find the executable.

gprofng/ChangeLog
2023-08-15  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

	* src/gp-display-text.cc (reexec): Use execvp instead of execv.