don't try to cross-compile sanitizer tests

this was a pre-existing latent bug, we just didn't have any CI builders exercising it.

fixes the following errors:
```
 ---- [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt1 stdout ----

error in revision `opt1`: test compilation failed although it shouldn't!
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=i686-unknown-linux-gnu" "--cfg" "opt1" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--remap-path-prefix=/checkout/tests/ui=fake-test-src-base" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/sanitize/new-llvm-pass-manager-thin-lto.opt1/a" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/i686-unknown-linux-gnu/native/rust-test-helpers" "-Clinker=x86_64-linux-gnu-gcc" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/sanitize/new-llvm-pass-manager-thin-lto.opt1/auxiliary" "-Zsanitizer=address" "-Clto=thin" "-Copt-level=1"
--- stderr -------------------------------
error: linking with `x86_64-linux-gnu-gcc` failed: exit status: 1
   = note: x86_64-linux-gnu-gcc: error: /checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/i686-unknown-linux-gnu/lib/librustc-nightly_rt.asan.a: No such file or directory

failures:
    [ui] tests/ui/sanitize/badfree.rs
    [ui] tests/ui/sanitize/address.rs
    [ui] tests/ui/sanitize/use-after-scope.rs
    [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt0
    [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt1
```

tests/ui/sanitize/address.rs

@@ -1,11 +1,12 @@
 // needs-sanitizer-support
 // needs-sanitizer-address
+// ignore-cross-compile
 //
 // compile-flags: -Z sanitizer=address -O -g
 //
 // run-fail
 // error-pattern: AddressSanitizer: stack-buffer-overflow
-// error-pattern: 'xs' (line 13) <== Memory access at offset
+// error-pattern: 'xs' (line 14) <== Memory access at offset
 
 use std::hint::black_box;
 

tests/ui/sanitize/badfree.rs

@@ -1,5 +1,6 @@
 // needs-sanitizer-support
 // needs-sanitizer-address
+// ignore-cross-compile
 //
 // compile-flags: -Z sanitizer=address -O
 //

tests/ui/sanitize/issue-72154-lifetime-markers.rs

@@ -5,6 +5,7 @@
 //
 // needs-sanitizer-support
 // needs-sanitizer-address
+// ignore-cross-compile
 //
 // compile-flags: -Copt-level=0 -Zsanitizer=address
 // run-pass

tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs

@@ -4,6 +4,7 @@
 //
 // needs-sanitizer-support
 // needs-sanitizer-address
+// ignore-cross-compile
 //
 // no-prefer-dynamic
 // revisions: opt0 opt1

tests/ui/sanitize/use-after-scope.rs

@@ -1,5 +1,6 @@
 // needs-sanitizer-support
 // needs-sanitizer-address
+// ignore-cross-compile
 //
 // compile-flags: -Zsanitizer=address
 // run-fail