Chapter 5. C Implementation-defined behavior
A conforming implementation of ISO C is required to document its
choice of behavior in each of the areas that are designated
"implementation defined." The following lists all such areas,
along with the section number from the ISO/IEC 9899:1999 standard.
[How a diagnostic is identified (3.10, 22.214.171.124).]
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 (126.96.36.199).]