disable s390x vector intrinsics if softfloat is enabled

we will add an explicit incompatibility of softfloat and vector feature
in rutsc s390x-unknown-none-softfloat target specification.
Therefore we need to disable vector intrinsics here to be able to compile
core for this target.

library/stdarch/crates/core_arch/src/s390x/mod.rs

@@ -2,6 +2,11 @@
 
 pub(crate) mod macros;
 
+/// the float and vector registers overlap therefore we cannot use any vector
+/// extensions if softfloat is enabled.
+
+#[cfg(not(target_abi = "softfloat"))]
 mod vector;
+#[cfg(not(target_abi = "softfloat"))]
 #[unstable(feature = "stdarch_s390x", issue = "130869")]
 pub use self::vector::*;