Remove checks against header guards.

It seems that this header conditionally tests whether <complex.h> is
included, as the 'complex' keyword is otherwise not available. This
version of math_private.h includes <complex.h> unconditionally, so there
is no need to test against this.

src/math_private.h

@@ -333,9 +333,7 @@ double	__kernel_sin(double,double,int);
 double	__kernel_cos(double,double);
 double	__kernel_tan(double,double,int);
 double	__ldexp_exp(double,int);
-#ifdef _COMPLEX_H
 double complex __ldexp_cexp(double complex,int);
-#endif
 
 /* float precision kernel functions */
 #ifdef INLINE_REM_PIO2F
@@ -355,9 +353,7 @@ __inline
 #endif
 float	__kernel_tandf(double,int);
 float	__ldexp_expf(float,int);
-#ifdef _COMPLEX_H
 float complex __ldexp_cexpf(float complex,int);
-#endif
 
 /* long double precision kernel functions */
 long double __kernel_sinl(long double, long double, int);