configure: Fix C++11 test with -Werror=missing-declarations
configure: Fix C++11 test with -Werror=missing-declarations

This fixes the following error (copied from config.log):

  conftest.cpp:49:14: error: no previous declaration for 'void
  test_template_alias_sfinae::test()' [-Werror=missing-declarations]

Signed-off-by: Uli Schlachter <346c0ad49ac8427b61b3b55abbe37dc0ebd524f2@znc.in>
(cherry picked from commit 2d1336dcf3d620f115aec771ddfb86b199a71e21)

dgw/znc,psychon/znc,Hasimir/znc,jpnurmi/znc,dgw/znc,wolfy1339/znc,aarondunlap/znc,BtbN/znc,TuffLuck/znc,Mikaela/znc,evilnet/znc,anthonyryan1/znc,evilnet/znc,evilnet/znc,Kriechi/znc,jpnurmi/znc,YourBNC/znc,KiNgMaR/znc,ollie27/znc,elyscape/znc,DarthGandalf/znc,jreese/znc,kashike/znc,TuffLuck/znc,Mikaela/znc,Phansa/znc,YourBNC/znc,jreese/znc,ollie27/znc,wolfy1339/znc,Adam-/znc,aarondunlap/znc,TuffLuck/znc,DarthGandalf/znc,elyscape/znc,Zarthus/znc,Hasimir/znc,GLolol/znc,TuffLuck/znc,znc/znc,anthonyryan1/znc,psychon/znc,Mikaela/znc,Mikaela/znc,reedloden/znc,markusj/znc,Kriechi/nobnc,reedloden/znc,ollie27/znc,Zarthus/znc,reedloden/znc,Hasimir/znc,KiNgMaR/znc,Mkaysi/znc,Phansa/znc,Mkaysi/znc,TuffLuck/znc,Hasimir/znc,wolfy1339/znc,BtbN/znc,elyscape/znc,Mkaysi/znc,Zarthus/znc,Phansa/znc,aarondunlap/znc,evilnet/znc,Adam-/znc,dgw/znc,Adam-/znc,TuffLuck/znc,KielBNC/znc,anthonyryan1/znc,jpnurmi/znc,kashike/znc,psychon/znc,badloop/znc,wolfy1339/znc,KielBNC/znc,elyscape/znc,badloop/znc,elyscape/znc,aarondunlap/znc,znc/znc,TuffLuck/znc,psychon/znc,markusj/znc,badloop/znc,psychon/znc,Phansa/znc,KiNgMaR/znc,Kriechi/znc,Kriechi/znc,KielBNC/znc,DarthGandalf/znc,kashike/znc,kashike/znc,evilnet/znc,Phansa/znc,jreese/znc,Adam-/znc,znc/znc,YourBNC/znc,KiNgMaR/znc,KiNgMaR/znc,Kriechi/nobnc,Hasimir/znc,markusj/znc,badloop/znc,jpnurmi/znc,reedloden/znc,jreese/znc,aarondunlap/znc,evilnet/znc,Kriechi/nobnc,Hasimir/znc,wolfy1339/znc,Mkaysi/znc,KielBNC/znc,BtbN/znc,Mikaela/znc,Adam-/znc,reedloden/znc,GLolol/znc,Hasimir/znc,jreese/znc,Zarthus/znc,jreese/znc,psychon/znc,BtbN/znc,dgw/znc,anthonyryan1/znc,Mkaysi/znc,znc/znc,markusj/znc,jpnurmi/znc,elyscape/znc,wolfy1339/znc,BtbN/znc,dgw/znc,kashike/znc,Mkaysi/znc,Zarthus/znc,Mkaysi/znc,Zarthus/znc,DarthGandalf/znc,KielBNC/znc,badloop/znc,Mikaela/znc,GLolol/znc,GLolol/znc,kashike/znc,YourBNC/znc,badloop/znc,DarthGandalf/znc,jpnurmi/znc,Adam-/znc,anthonyryan1/znc,GLolol/znc,znc/znc,KielBNC/znc,YourBNC/znc,ollie27/znc,Phansa/znc,KiNgMaR/znc,BtbN/znc,Kriechi/znc,DarthGandalf/znc,Kriechi/znc,Mikaela/znc,markusj/znc,jpnurmi/znc,Kriechi/znc,reedloden/znc,anthonyryan1/znc,aarondunlap/znc,aarondunlap/znc,ollie27/znc,markusj/znc,dgw/znc,badloop/znc,YourBNC/znc,anthonyryan1/znc,znc/znc,ollie27/znc,Adam-/znc,GLolol/znc