Check whether -D_FORTIFY_SOURCE=2 can be added to CPPFLAGS without macro redefinition warnings. Some distributions (such as Gentoo Linux) enable _FORTIFY_SOURCE globally in their compilers, leading to unnecessary warnings in the form of
<command-line>:0:0: error: "_FORTIFY_SOURCE" redefined [-Werror] <built-in>: note: this is the location of the previous definition
which is a problem if -Werror is enabled. This macro checks whether _FORTIFY_SOURCE is already defined, and if not, adds -D_FORTIFY_SOURCE=2 to CPPFLAGS.
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Copyright © 2017 David Seifert firstname.lastname@example.org
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