[patch] Factor common code for C-family and Fortran preprocessing (3rd try)

[Joseph S. Myers]

On Fri, 1 Oct 2010, FX wrote:

> Please find attached my third try to this patch, taking into account Joseph's comment.
> 
> Bootstrapped and regtested on x86_64-darwin. OK to commit?

The C changes are OK.  There are more macros I would think of as 
language-independent - __EXCEPTIONS, __USING_SJLJ_EXCEPTIONS__, 
__GCC_HAVE_DWARF2_CFI_ASM, __SSP_ALL__, __SSP__, _OPENMP, __NO_INLINE__, 
__SIZEOF_INT128__ at least - but they can be dealt with later.

-- 
Joseph S. Myers
joseph@codesourcery.com