compile detection of powf, etc

Is there a standard way using the preprocessor to detect if a given C
compiler/library environment provides the C99 <math.h> floating point
functions such as:

float powf(float x, float y);
float sqrtf(float x);
etc

so we could "provide" these prototypes or not via our

"xtra_math.h" file

Note some C environments are incomplete and may define the C90 flag but
still provide these functions. So I think we need to check each
function.

looking for any suggestions

thanks

.

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