IPA's C source code relies on some non-standard features that are not available by default. So far the C code compiles fine because we rely on GCC with GNU extensions.

• On Fedora 30, Samba uses memset_s from C11. The C11 extensions can be enabled with by using a C11 compiler (-std=c11) or __STDC_WANT_LIB_EXT1__=1.
• strndup() is only defined by string.h with _POSIX_C_SOURCE=200809L or higher, see _POSIX_C_SOURCE >= 200809
• htole16() is only defined by endian.h when _DEFAULT_SOURCE is defined, see htole16()
• time_t is not defined by default. Code needs to include time.h.
• typeof() is a GNU extension. There is the more generic __typeof__() extension. IPA uses only two calls to typeof(), both can be easily replaced by explicit type names.

All feature macros must be defined before including a header file. Since a lot of C files don't include config.h, it's easier to define the feature macros on the command line than in the project's config header file.

Thomas discovered the memset_s issue when mass-rebuild of F30 failed, http://koji.fedoraproject.org/koji/buildinfo?buildID=1186722