Disable jemalloc tests on platforms where it is disabled (closes rust-lang#38612)

See also rust-lang#37392

Author: infinity0

src/test/compile-fail/allocator-rust-dylib-is-jemalloc.rs

@@ -29,9 +29,11 @@ extern crate allocator_dylib2;
 // ensure we get the same error.
 //
 // So long as we CI linux/OSX we should be good.
-#[cfg(any(target_os = "linux", target_os = "macos"))]
+#[cfg(any(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64")),
+          target_os = "macos"))]
 extern crate alloc_system;
-#[cfg(not(any(target_os = "linux", target_os = "macos")))]
+#[cfg(not(any(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64")),
+              target_os = "macos")))]
 extern crate allocator1;
 
 fn main() {

src/test/run-pass/allocator-default.rs

@@ -10,7 +10,8 @@
 
 #![feature(alloc_jemalloc)]
 
-#[cfg(any(target_os = "linux", target_os = "macos"))]
+#[cfg(any(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64")),
+          target_os = "macos"))]
 extern crate alloc_jemalloc;
 
 fn main() {