improve handling of --help
improve handling of --help

  Previously ./configure --prefix=/foo --help didn't show the help-text

Signed-off-by: Bernhard Reutner-Fischer <ce1ac9e9ad16abccd7821f371ad381197b4768ac@gmail.com>

seyko2/tinycc,gfwilliams/tinycc,andrewchambers/tccmirror,metaeducation/tcc,acook/tinycc,metaeducation/tcc,fstudio/tinycc,mobiphil/tinnycc,Wallbraker/DCPU-TCC,andreiw/tinycc,mitake/tinycc,leeduhem/tinycc,andreiw/tinycc,Archs/TinyCC,run4flat/tinycc,leeduhem/tinycc,Saectar/inherpreter,rchandramouli/tinycc,shinh/nacltcc,yousong/tinycc,Archs/TinyCC,mitake/tinycc,rchandramouli/tinycc,mirror/tinycc,Saectar/inherpreter,mirror/tinycc,soywiz/tinycc,andrewchambers/tccmirror,rchandramouli/tinycc,gfwilliams/tinycc,xcm/tcc,fstudio/tinycc,Archs/TinyCC,shinh/nacltcc,run4flat/tinycc,soywiz/tinycc,mitake/tinycc,andrewchambers/tccmirror,acook/tinycc,mobiphil/tinnycc,Archs/TinyCC,ftdi-paul-jiao/tinyCC,melkior/tinycc,andrewchambers/tccmirror,yousong/tinycc,code4game/tinycc,shinh/nacltcc,mingodad/tinycc,alfonsokim/tinycc,alfonsokim/tinycc,shinh/nacltcc,gfwilliams/tinycc,melkior/tinycc,code4game/tinycc,avih/tinycc,metaeducation/tcc,FriedBreakfast/tcc,Archs/TinyCC,alfonsokim/tinycc,acook/tinycc,yousong/tinycc,soywiz/tinycc,acook/tinycc,Wallbraker/DCPU-TCC,seyko2/tinycc,ftdi-paul-jiao/tinyCC,rchandramouli/tinycc,mirror/tinycc,avih/tinycc,FriedBreakfast/tcc,metaeducation/tcc,fstudio/tinycc,FriedBreakfast/tcc,gfwilliams/tinycc,mobiphil/tinnycc,leeduhem/tinycc,Saectar/inherpreter,melkior/tinycc,avih/tinycc,alfonsokim/tinycc,mingodad/tinycc,leeduhem/tinycc,run4flat/tinycc,avih/tinycc,seyko2/tinycc,fstudio/tinycc,Saectar/inherpreter,soywiz/tinycc,alfonsokim/tinycc,fstudio/tinycc,xcm/tcc,mingodad/tinycc,seyko2/tinycc,Saectar/inherpreter,xcm/tcc,run4flat/tinycc,Wallbraker/DCPU-TCC,FriedBreakfast/tcc,leeduhem/tinycc,yousong/tinycc,andreiw/tinycc,gfwilliams/tinycc,ftdi-paul-jiao/tinyCC,andrewchambers/tccmirror,mingodad/tinycc,run4flat/tinycc,melkior/tinycc,ftdi-paul-jiao/tinyCC,mobiphil/tinnycc,mitake/tinycc,FriedBreakfast/tcc,melkior/tinycc,mirror/tinycc,metaeducation/tcc,seyko2/tinycc,rchandramouli/tinycc,shinh/nacltcc,code4game/tinycc