The attached test case has these lines ...

int builtin_array[100];
std::array<int, 100> std_array;

Build it and search the assembly for the lines that put each array in a section.

$ tiarmclang -S file.cpp

$ findstr section file.s | findstr array
        .section        .bss.builtin_array,"aw",%nobits
        .section        .data.std_array,"aw",%progbits

The builtin_array is in an uninitialized section. The std_array is in an initialized section. They should both be in an uninitialized section.