[Bug c++/23139] [3.4/4.0/4.1 Regression] -pedantic -ffast-math breaks working code

[Gabriel Dos Reis]

"mmitchel at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| The problem behind both diagnostics fact that the C++ front-end pre-lexes the
| entire source file.  As a result, the lexing routines, which depends on the
| setting of pedantic to determine whether or not to issue errors, are
| called when pedantic is set, even though we are within an
| __extension__ block.  Because the parsing of __extension__ blocks is
| complex, we need to either (a) eliminate the up-front lexing, or (b)
| defer issuing diagnostics until we are actually in 
| position to know the correct value of pedantic.

In long term, I believe (b) is a better alternative.

-- Gaby