How a diagnostic is identified (C90 3.7, C99 3.10, C90 and C99 5.1.1.3).
Diagnostics consist of all the output sent to stderr by GCC.
Whether each nonempty sequence of white-space characters other than
new-line is retained or replaced by one space character in translation
phase 3 (C90 and C99 5.1.1.2).