[build] rework platform/default directory and add -files.txt for vendored libs

platform/default/src/mbgl/util/string_stdlib.cpp

@@ -0,0 +1,74 @@
+#include <mbgl/util/platform.hpp>
+#include <libnu/casemap.h>
+#include <cstring>
+#include <sstream>
+
+namespace mbgl { namespace platform {
+
+std::string uppercase(const std::string& str)
+{
+    std::stringstream output;
+    char const *itr = str.c_str(), *nitr;
+    char const *end = itr + str.length();
+    char lo[5] = { 0 };
+
+    for (; itr < end; itr = nitr)
+    {
+        uint32_t code_point = 0;
+        char const* buf = nullptr;
+
+        nitr = _nu_toupper(itr, end, nu_utf8_read, &code_point, &buf, nullptr);
+        if (buf != nullptr)
+        {
+            do
+            {
+                buf = NU_CASEMAP_DECODING_FUNCTION(buf, &code_point);
+                if (code_point == 0) break;
+                output.write(lo, nu_utf8_write(code_point, lo) - lo);
+            }
+            while (code_point != 0);
+        }
+        else
+        {
+            output.write(itr, nitr - itr);
+        }
+    }
+
+    return output.str();
+
+}
+
+std::string lowercase(const std::string& str)
+{
+    std::stringstream output;
+    char const *itr = str.c_str(), *nitr;
+    char const *end = itr + str.length();
+    char lo[5] = { 0 };
+
+    for (; itr < end; itr = nitr)
+    {
+        uint32_t code_point = 0;
+        char const* buf = nullptr;
+
+        nitr = _nu_tolower(itr, end, nu_utf8_read, &code_point, &buf, nullptr);
+        if (buf != nullptr)
+        {
+            do
+            {
+                buf = NU_CASEMAP_DECODING_FUNCTION(buf, &code_point);
+                if (code_point == 0) break;
+                output.write(lo, nu_utf8_write(code_point, lo) - lo);
+            }
+            while (code_point != 0);
+        }
+        else
+        {
+            output.write(itr, nitr - itr);
+        }
+    }
+
+    return output.str();
+}
+
+} // namespace platform
+} // namespace mbgl