That depends on how you define "presence" and "free software code". To cite from the article: "The GNU C Library is used as the C library in the GNU systems and

That depends on how you define "presence" and "free software code". To cite from the article: "The GNU C Library is used as the C library in the GNU systems and is widely used on systems with the Linux kernel." That means that glibc is mostly used as part of desktop/server Linux distributions and not directly by software (although there is significant amount of both free and non-free software that depends on glibc-specific extensions or behavior).