[Committed, AArch64] Disable tests for ilp32.

[Committed, AArch64] Disable tests for ilp32.

Currently Return Address Signing is only supported in lp64. Thus the
tests that I added recently (that enables return address signing by the
mbranch-protection=standard option), should also be exempted from testing in
ilp32. This patch adds the needed dg-require-effective-target directive in the
tests.

*** gcc/testsuite/ChangeLog ***

2019-01-10  Sudakshina Das  <sudi.das@arm.com>

	* gcc.target/aarch64/bti-1.c: Exempt for ilp32.
	* gcc.target/aarch64/bti-2.c: Likewise.
	* gcc.target/aarch64/bti-3.c: Likewise.

Committed as obvious.

From-SVN: r267818