Michael Felt wrote:
> Curious why you are calling this a compiler bug.

Because it is a compiler bug.  Try to compile (but not link) the 
attached file.  Here's what I get on AIX 7.1 with xlc 12.1 and GCC 4.8.1.

$ gcc -c xlcbug1.c
$ xlc -c xlcbug1.c
"xlcbug1.c", line 22.39: 1506-045 (S) Undeclared identifier 
GL_FLT_PREC_BOUND.
"xlcbug1.c", line 22.23: 1506-1324 (S) Array size must have integer type.

There's nothing wrong with the program.  The identifier is properly 
declared.

> What is the origin of the _GL_* identifiers?

They're from Gnulib, but that's irrelevant to the compiler bug, as the 
attached file demonstrates.