[gdb/testsuite] Require c++11 where necessary

[gdb/testsuite] Require c++11 where necessary

When building gdb on ubuntu 16.04 with gcc 5.4.0, and running the gdb
testsuite we run into failures due test-cases requiring at least c++1.

Fix this by adding -std=c++11 to those test-cases.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2019-05-21  Tom de Vries  <tdevries@suse.de>

	* gdb.arch/amd64-eval.exp: Require c++11.
	* gdb.base/max-depth.exp: Same.
	* gdb.compile/compile-cplus-array-decay.exp: Same.
	* gdb.cp/meth-typedefs.exp: Same.
	* gdb.cp/subtypes.exp: Same.
	* gdb.cp/temargs.exp: Same.