Enable larger page size in jemalloc

Fixes #850

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ### Build
 
+Incrased the default page size of Jemalloc, so difftastic should work
+on systems with large page sizes (typically aarch64, i.e. Arm).
+
 difftastic now requires Rust 1.75 to build.
 
 ### Parsing

build.rs

@@ -220,6 +220,14 @@ fn main() {
     if let Some((version, _, _)) = rustc::triple() {
         println!("cargo:rustc-env=DFT_RUSTC_VERSION={}", version);
     }
+
+    // Use 64-KiB pages with jemalloc. This solves "<jemalloc>:
+    // Unsupported system page size" errors, and performs the same as
+    // jemalloc's default settings.
+    //
+    // Note that difftastic does not use jemalloc on all operating
+    // systems, but it's harmless to set this unconditionally.
+    println!("cargo:rustc-env=JEMALLOC_SYS_WITH_LG_PAGE=16");
 }
 
 fn commit_info() {