Avoid warnings emession on re-importing Font::FreeType

Without patch there are irritating warnings, without possibility to track warnings source and fix it.

```
$ perl -I lib -I blib/arch -e 'use Font::FreeType; use Font::FreeType;'
Constant subroutine FT_LOAD_DEFAULT redefined at -e line 4294967295.
Constant subroutine FT_LOAD_NO_SCALE redefined at -e line 4294967295.
Constant subroutine FT_LOAD_NO_HINTING redefined at -e line 4294967295.
Constant subroutine FT_LOAD_NO_BITMAP redefined at -e line 4294967295.
Constant subroutine FT_LOAD_VERTICAL_LAYOUT redefined at -e line 4294967295.
Constant subroutine FT_LOAD_FORCE_AUTOHINT redefined at -e line 4294967295.
Constant subroutine FT_LOAD_CROP_BITMAP redefined at -e line 4294967295.
Constant subroutine FT_LOAD_PEDANTIC redefined at -e line 4294967295.
Constant subroutine FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH redefined at -e line 4294967295.
Constant subroutine FT_LOAD_IGNORE_TRANSFORM redefined at -e line 4294967295.
Constant subroutine FT_LOAD_LINEAR_DESIGN redefined at -e line 4294967295.
Constant subroutine FT_LOAD_NO_AUTOHINT redefined at -e line 4294967295.
Constant subroutine FT_RENDER_MODE_NORMAL redefined at -e line 4294967295.
Constant subroutine FT_RENDER_MODE_LIGHT redefined at -e line 4294967295.
Constant subroutine FT_RENDER_MODE_MONO redefined at -e line 4294967295.
Constant subroutine FT_RENDER_MODE_LCD redefined at -e line 4294967295.
Constant subroutine FT_RENDER_MODE_LCD_V redefined at -e line 4294967295.
Constant subroutine FT_KERNING_DEFAULT redefined at -e line 4294967295.
Constant subroutine FT_KERNING_UNFITTED redefined at -e line 4294967295.
Constant subroutine FT_KERNING_UNSCALED redefined at -e line 4294967295.
```

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