bootstrap: Build jemalloc with support for 64K pages

By default, jemalloc is built to only support the same page size as the
host machine. 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 +1207,10 @@ pub fn rustc_cargo_env(
             rustc_llvm_env(builder, cargo, target)
         }
     }
+
+    if builder.config.jemalloc {
+        cargo.env("JEMALLOC_SYS_WITH_LG_PAGE", "16");
+    }
 }
 
 /// Pass down configuration from the LLVM build into the build of