For cproj test-case, use glibc version xfail

For cproj test-case, use glibc version xfail

2014-08-04  Tom de Vries  <tom@codesourcery.com>

	* gcc.dg/cproj-fails-with-broken-glibc.c: Use xfail for broken glibc
	version instead of required-target.
	* lib/target-supports.exp
	(check_effective_target_not_glibc_2_11_or_earlier): Replace by ...
	(check_effective_target_glibc_2_11_or_earlier): ... this.

	* doc/sourcebuild.texi (glibc, glibc_2_12_or_later)
	(glibc_2_11_or_earlier): Document effective-target keywords.

From-SVN: r213693