"Applications should note that the standard PATH to the shell cannot be assumed to be either /bin/sh or /usr/bin/sh, and should be determined by interrogation of the PATH returned by getconf PATH , ensuring that the returned pathname is an absolute pathname and not a shell built-in."
#define SHELL_PATH "/bin/sh" /* Path of the shell. */
Thus any application that uses system() is violating the above section.
glibc is not an application, it is part of the system that defines the location
of the shell.
No, glibc is not an application, but it causes any application that uses system() to assume that the path to the shell is /bin/sh rather than interrogating PATH.