android: use jemalloc on Android (#32273)

This is a fix for the crash issue in 64-bit ARM [#32175][1].

When targeting Android 11 and above, 64-bit ARM platforms
have the 'Tagged Pointer' feature enabled by default which
causes memory allocated using the system allocator to have
a non-zero 'tag' set in the highest byte of heap addresses.

This is incompatible with SpiderMonkey which assumes that
only the bottom 48 bits are set and asserts this at various
points.

Both Servo and Gecko have a similar architecture where
the pointer to a heap allocated DOM struct is encoded as
a JS::Value and stored in the DOM_OBJECT_SLOT (reserved
slot) of the JSObject which reflects the native DOM struct.

As observed in #32175, even Gecko crashes with `jemalloc`
disabled which suggests that support for using the native
system allocator with tagged pointers enabled by default
is not present at the moment.

[1]: https://github.com/servo/servo/issues/32175

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/allocator/lib.rs

@@ -9,12 +9,7 @@ static ALLOC: Allocator = Allocator;
 
 pub use crate::platform::*;
 
-#[cfg(not(any(
-    windows,
-    target_os = "android",
-    feature = "use-system-allocator",
-    target_env = "ohos"
-)))]
+#[cfg(not(any(windows, feature = "use-system-allocator", target_env = "ohos")))]
 mod platform {
     use std::os::raw::c_void;
 
@@ -37,11 +32,7 @@ mod platform {
 
 #[cfg(all(
     not(windows),
-    any(
-        target_os = "android",
-        feature = "use-system-allocator",
-        target_env = "ohos"
-    )
+    any(feature = "use-system-allocator", target_env = "ohos")
 ))]
 mod platform {
     pub use std::alloc::System as Allocator;