tree-cfg.c (gimple_redirect_edge_and_branch): Create the decl label for the new dest block on demand.

* tree-cfg.c (gimple_redirect_edge_and_branch) <case GIMPLE_ASM>:
Create the decl label for the new dest block on demand.  Require
a fallthrough edge if no asm labels were redirected.

From-SVN: r154213