* lib/target-libpath.exp (set_gcc_exec_prefix_env_var,
	restore_gcc_exec_prefix_env_var): New procedures.
	(set_ld_library_path_env_vars,
	restore_ld_library_path_env_vars): Use them.
	* lib/c-compat.exp: Load target-libpath.exp.
	(compat-use-alt-compiler): Call restore_gcc_exec_prefix_env_var.
	(compat-use-tst-compiler): Call set_gcc_exec_prefix_env_var.
	* g++.dg/compat/compat.exp (compat-use-alt-compiler): Call
	restore_gcc_exec_prefix_env_var.
	* g++.dg/compat/struct-layout-1.exp (compat-use-alt-compiler):
	Likewise.

From-SVN: r211093