avutil/libm: Replace macro based fminf() by function

This avoids issues when the FFMIN parameter evaluation has side effects
Reviewed-by: Clément Bœsch <u@pkh.me>
Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/libm.h

@@ -84,7 +84,10 @@ static av_always_inline float cbrtf(float x)
 
 #if !HAVE_FMINF
 #undef fminf
-#define fminf(x, y) (FFMIN(x,y))
+static av_always_inline av_const float fminf(float x, float y)
+{
+    return FFMIN(x, y);
+}
 #endif
 
 #if !HAVE_ISINF