#7 Implicit declaration of readlink due to _POSIX_*_SOURCE macro changes (C99 compatibility)

[Florian Weimer]

The attached patch addresses compilation failures with future compilers that do not support implicit function declarations.

Related to:

• https://fedoraproject.org/wiki/Changes/PortingToModernC
• https://fedoraproject.org/wiki/Toolchain/PortingToModernC