opt/eval: Include mathematics.h for NAN/INFINITY

These files use NAN/INFINITY but didn't include mathematics.h to get
the fallback definitions if the system lacks the macros.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/eval.c

@@ -29,6 +29,7 @@
 #include "avutil.h"
 #include "eval.h"
 #include "log.h"
+#include "mathematics.h"
 
 typedef struct Parser {
     const AVClass *class;

libavutil/opt.c

@@ -31,6 +31,7 @@
 #include "eval.h"
 #include "dict.h"
 #include "log.h"
+#include "mathematics.h"
 
 #if FF_API_FIND_OPT
 //FIXME order them and do a bin search