Replace non-leading tabs with spaces, using:

find -type f |  # list all regular files
  grep -E '\.(h|cpp|mm)$' |  # filter for source files
  grep -v '/mt_' |  # filter out generated files
  grep -v '/vendor/' | # and vendored GL
  xargs -n 1 -P $(nproc) ./replace_non_leading_tabs.lua  # reformat everything

source/Irrlicht/CFileSystem.cpp

@@ -21,7 +21,7 @@
 
 #if defined(_IRR_WINDOWS_API_)
 #include <direct.h> // for _chdir
-#include <io.h>		// for _access
+#include <io.h>     // for _access
 #include <tchar.h>
 #elif (defined(_IRR_POSIX_API_) || defined(_IRR_OSX_PLATFORM_) || defined(_IRR_ANDROID_PLATFORM_))
 #include <cstdio>