Test if host compiler supports -std=c++11 in ms-sysv.exp

2017-05-30  Tom de Vries  <tom@codesourcery.com>

	PR testsuite/80910
	* gcc.target/x86_64/abi/ms-sysv/ms-sysv.exp: Exit with status
	unsupported if host compiler does not support c++11.
	(host_supports_c++11): New proc.

From-SVN: r248701