Analyse following RPM build log snippet. Describe contents accurately, without speculation or suggestions for resolution.            
Your analysis must be as concise as possible, while keeping relevant information intact.
Snippet: 
sdl.c:717:16: warning: incompatible implicit declaration of built-in function âfabsfâ [-Wbuiltin-declaration-mismatch]
  717 |     float d0 = fabsf(fasp - asp);
      |                ^~~~~
This is compiler warning. Function `fabsf` which is normally builtin, was implicitly declared in the file `sdl.c`. This is not allowed in C programming language.