Skip the test if arm7a is not supported at link time. This is the case
if the toolchain targets an M-profile CPU by default and does not have
A-profile multilib: the link step fails because it tries to mix
M-profile startup files with A-profile testcase.

2020-02-24  Christophe Lyon  <christophe.lyon@linaro.org>

	PR lto/78353
	* gcc.target/arm/pr78353-1.c: Add arm_arch_v7a_multilib effective
	target.
	* gcc.target/arm/pr78353-2.c: Likewise.