bootstrap: Build jemalloc for AArch64 with support for 64K pages

By default, jemalloc is built to only support the same page size as the
host machine. For AArch64 targets, set an env variable so that jemalloc
is built with support for page sizes up to 64K regardless of the host machine.

Author: mrkajetanp

src/bootstrap/src/core/build_steps/compile.rs

@@ -1207,6 +1207,13 @@ pub fn rustc_cargo_env(
             rustc_llvm_env(builder, cargo, target)
         }
     }
+
+    if builder.config.jemalloc
+        && target.starts_with("aarch64")
+        && env::var_os("JEMALLOC_SYS_WITH_LG_PAGE").is_none()
+    {
+        cargo.env("JEMALLOC_SYS_WITH_LG_PAGE", "16");
+    }
 }
 
 /// Pass down configuration from the LLVM build into the build of