[3.x] Fix FreeType crashing in GCC + LTO builds.

[bruvzg]

Seems like GCC LTO is not playing nice with setjmp/longjmp and removing a bunch of code, this PR adds assign to the dummy volatile variable to prevent optimization.

Fixes #61499

[akien-mga]

I assume this might be needed in master too.

[bruvzg]

I assume this might be needed in master too.

Probably yes.

[akien-mga]

Thanks!

[EzraT]

Thank you!

[apodtele]

What this work?

   gray_convert_glyph_inner( RAS_ARG,
                             int  continued )
   {
-    int  error;
+    volatile int  error;


     if ( ft_setjmp( ras.jump_buffer ) == 0 )