os: Add helper to find host temp directory

renderdoc/os/os_specific.h

@@ -233,6 +233,7 @@ void GetDefaultFiles(const char *logBaseName, string &capture_filename, string &
                      string &target);
 string GetHomeFolderFilename();
 string GetAppFolderFilename(const string &filename);
+string GetTempFolderFilename();
 string GetReplayAppFilename();
 
 void CreateParentDirectory(const string &filename);

renderdoc/os/posix/posix_stringio.cpp

@@ -59,6 +59,11 @@ string GetHomeFolderFilename()
   return homedir;
 }
 
+string GetTempFolderFilename()
+{
+  return string(GetTempRootPath()) + "/";
+}
+
 void CreateParentDirectory(const string &filename)
 {
   string fn = dirname(filename);

renderdoc/os/win32/win32_stringio.cpp

@@ -328,6 +328,15 @@ string GetAppFolderFilename(const string &filename)
   return ret;
 }
 
+string GetTempFolderFilename()
+{
+  wchar_t temp_filename[MAX_PATH];
+
+  GetTempPathW(MAX_PATH, temp_filename);
+
+  return StringFormat::Wide2UTF8(wstring(temp_filename));
+}
+
 uint64_t GetModifiedTimestamp(const string &filename)
 {
   wstring wfn = StringFormat::UTF82Wide(filename);