[testsuite] Avoid Tcl 8.5-specific behavior

[testsuite] Avoid Tcl 8.5-specific behavior

	gcc/
	* doc/install.texi (Prerequisites) <Tcl>: Add comment.
	gcc/testsuite/
	* c-c++-common/goacc/kernels-decompose-1.c: Avoid Tcl 8.5-specific
	behavior.
	* c-c++-common/goacc/kernels-decompose-2.c: Likewise.
	* gfortran.dg/goacc/kernels-decompose-1.f95: Likewise.
	* gfortran.dg/goacc/kernels-decompose-2.f95: Likewise.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/kernels-decompose-1.c: Avoid
	Tcl 8.5-specific behavior.
	* testsuite/libgomp.oacc-fortran/pr94358-1.f90: Likewise.

Reported-by: David Edelsohn <dje.gcc@gmail.com>