If I understand correctly what bugs you are talking about,
most (all?) of those were solved in the dark ages already
(i.e., the 3.x series).
Alas, no. gcc is amazingly (and inconsistently) sloppy about the
things it accepts as integer constant expressions.
It certainly is not a valid C
Why not? Nothing in the C standard says all your externs
have to be defined in some other translation unit you link
with AFAIK.
It's not about externs. It's about things like
unsigned n;
int a[] = {[n - n + n - n] = 1};
And yes, gcc does eat that.
With -pedantic -std=c99, at that.
However,
unsigned n;
int a[] = {[n + n - n - n] = 1};
gets you error: nonconstant array index in initializer
And that's 4.1, not 3.x...