Add <cfloat> for missing DBL_MAX declaration (#6582)

Fixes build on linux/gcc10.

src/libslic3r/PrintApply.cpp

@@ -1,6 +1,8 @@
 #include "Model.hpp"
 #include "Print.hpp"
 
+#include <cfloat>
+
 namespace Slic3r {
 
 // Add or remove support modifier ModelVolumes from model_object_dst to match the ModelVolumes of model_object_new

src/libslic3r/SlicingAdaptive.cpp

@@ -4,6 +4,7 @@
 #include "SlicingAdaptive.hpp"
 
 #include <boost/log/trivial.hpp>
+#include <cfloat>
 
 // Based on the work of Florens Waserfall (@platch on github)
 // and his paper