[core] don't use <boost/functional/hash.hpp> to avoid <locale> include

src/mbgl/util/font_stack.cpp

@@ -1,8 +1,8 @@
 #include <mbgl/util/font_stack.hpp>
 #include <mbgl/util/logging.hpp>
 #include <mbgl/style/layers/symbol_layer_impl.hpp>
+#include <mbgl/util/hash.hpp>
 
-#include <boost/functional/hash.hpp>
 #include <boost/algorithm/string/join.hpp>
 
 namespace mbgl {
@@ -14,7 +14,11 @@ std::string fontStackToString(const FontStack& fontStack) {
 }
 
 FontStackHash FontStackHasher::operator()(const FontStack& fontStack) const {
-    return boost::hash_range(fontStack.begin(), fontStack.end());
+    std::size_t seed = 0;
+    for (const auto& font : fontStack) {
+        util::hash_combine(seed, font);
+    }
+    return seed;
 }
 
 std::set<FontStack> fontStacks(const std::vector<Immutable<style::Layer::Impl>>& layers) {