tcctest: One more signed zero test
tcctest: One more signed zero test

This also checks that -(-0.0) is +0.0.

metaeducation/tcc,andrewchambers/tccmirror,andrewchambers/tccmirror,code4game/tinycc,rchandramouli/tinycc,fstudio/tinycc,fstudio/tinycc,leeduhem/tinycc,mingodad/tinycc,run4flat/tinycc,avih/tinycc,code4game/tinycc,gfwilliams/tinycc,gfwilliams/tinycc,andrewchambers/tccmirror,fstudio/tinycc,leeduhem/tinycc,fstudio/tinycc,run4flat/tinycc,mirror/tinycc,alfonsokim/tinycc,leeduhem/tinycc,rchandramouli/tinycc,code4game/tinycc,run4flat/tinycc,metaeducation/tcc,alfonsokim/tinycc,rchandramouli/tinycc,avih/tinycc,fstudio/tinycc,seyko2/tinycc,metaeducation/tcc,gfwilliams/tinycc,avih/tinycc,mingodad/tinycc,alfonsokim/tinycc,andreiw/tinycc,rchandramouli/tinycc,seyko2/tinycc,leeduhem/tinycc,andreiw/tinycc,seyko2/tinycc,andreiw/tinycc,mirror/tinycc,gfwilliams/tinycc,avih/tinycc,seyko2/tinycc,run4flat/tinycc,leeduhem/tinycc,gfwilliams/tinycc,run4flat/tinycc,andrewchambers/tccmirror,rchandramouli/tinycc,mingodad/tinycc,mingodad/tinycc,alfonsokim/tinycc,metaeducation/tcc,seyko2/tinycc,metaeducation/tcc,mirror/tinycc,alfonsokim/tinycc,andrewchambers/tccmirror,mirror/tinycc