Why it is allowed to initialize static variable with non const here?

Question

I was reading this. The first answer by @Andrei T says that

A \"large\" object is never a constant expression in C, even if the object is declared a

Answer 1

It's because the ideone likely invokes gcc with -O option (optimization level 1). This is the case even for older versions of gcc (mine is 4.4.7):

$ gcc -ansi main.c 
main.c: In function ‘main’:
main.c:6: error: initializer element is not constant
$ gcc -ansi -O main.c
$ echo $?
0

What's interesting here is that with -pedantic it is working properly again and required diagnostic message is present (tested only with 4.4.7, _{see Keith's comment}):

gcc -ansi -pedantic -O main.c 
main.c: In function ‘main’:
main.c:6: error: initializer element is not constant
$ echo $?
1

Answer 2

This seems to be a gcc speciality. Compiling with -std=c89 or -pedantic reports the error.

Since in all C standards this is a constraint violation, not giving a diagnostic for that case makes gcc without one of the -std=c?? options a non-conforming compiler.