As the description in Builtins.def says: "e = const, but only when -fmath-errno=0".
This is step 2 of 3 to fix builtins and math calls as discussed in D39204.
I went through the lists at:
...and changed all of the builtins that correspond to functions that could set errno.
The math.h functions that are specified to never set errno are:
And for complex.h:
powi is not a standard libm function, so that's also left as "Fnc".