pr94780.c fails with ICE on aarch64 [PR94820]

pr94780.c fails with ICE on aarch64 [PR94820]

This is a simple fix for pr94820.
The PR was only fixed on i386, the same error was also reported on aarch64.
This function, because it is sometimes called even outside of function bodies, uses create_tmp_var_raw rather than create_tmp_var.
But in order for that to work, when first referenced, the VAR_DECLs need to appear in a TARGET_EXPR so that during gimplification
the var gets the right DECL_CONTEXT and is added to local decls. Without that, e.g. tree-nested.c ICEs on those.

2020-04-29  Haijian Zhang  <z.zhanghaijian@huawei.com>

	PR target/94820
	* config/aarch64/aarch64-builtins.c
	(aarch64_atomic_assign_expand_fenv): Use TARGET_EXPR instead of
	MODIFY_EXPR for first assignment to fenv_cr, fenv_sr and
	new_fenv_var.