Include what the new code uses

The Windows build stopped on test_kdtree.cpp: it calls std::iota without
including <numeric>, which libstdc++ happens to pull in anyway. Added
there, and the same for <limits> and <algorithm>/<cmath> where the
recent changes rely on them being included by something else.

src/libslic3r/ClipperUtils.cpp

@@ -1,3 +1,5 @@
+#include <algorithm>
+#include <cmath>
 #include <limits>
 #include <numeric>
 #include <unordered_map>

src/libslic3r/GCode/SeamPlacer.cpp

@@ -8,6 +8,7 @@
 #include <boost/log/trivial.hpp>
 #include <random>
 #include <algorithm>
+#include <limits>
 #include <queue>
 #include <unordered_map>
 

tests/libslic3r/test_kdtree.cpp

@@ -1,5 +1,6 @@
 #include <catch2/catch_all.hpp>
 
+#include <numeric>
 #include <random>
 #include <vector>