Fix no-complex build for bml_elemental code

[jeanlucf22]

No description provided.

[nicolasbock]

Why change that to _Complex? They are the same but we are using complex everywhere else in the library.

[jeanlucf22]

We are using _Complex in https://github.com/lanl/bml/blob/master/src/typed.h

[nicolasbock]

Ah true, I missed that. But we are also using complex here

bml/src/C-interface/ellpack/bml_elemental_ellpack.c

Lines 82 to 86 in ad26f0b

	float complex
	bml_get_element_ellpack_single_complex(
	bml_matrix_ellpack_t * A,
	int i,
	int j)

for example.

Let's merge this PR then as it is and then follow up with a clean up so that the use of comple / _Complex is consistent throughout.

While _Complex is equivalent to complex the former is never mentioned in any API documentation. For example:

CABS(3)

NAME
       cabs, cabsf, cabsl - absolute value of a complex number

SYNOPSIS
       #include <complex.h>

       double cabs(double complex z);
       float cabsf(float complex z);
       long double cabsl(long double complex z);

       Link with -lm.

Also, symbols with preceding _ are typically interpreted as internal symbols not meant for external use.

To make a long story short, I would prefer the consistent use of complex 😄