Support building big-endian objects (#2382)

The JIT build_object routine currently rejects building object files
for any big-endian platform.  However, most of the object builder
code works fine for either byte order, with the exception of a small
change in the ObjectBuilderTarget::new routine.

This patch adds that change and removes the assert in build_object.

crates/obj/src/builder.rs

@@ -122,10 +122,6 @@ fn process_unwind_info(info: &UnwindInfo, obj: &mut Object, code_section: Sectio
 
 /// Builds ELF image from the module `Compilation`.
 // const CODE_SECTION_ALIGNMENT: u64 = 0x1000;
-// assert_eq!(
-//     isa.triple().architecture.endianness(),
-//     Ok(target_lexicon::Endianness::Little)
-// );
 
 /// Iterates through all `LibCall` members and all runtime exported functions.
 #[macro_export]
@@ -223,7 +219,10 @@ impl ObjectBuilderTarget {
         Ok(Self {
             binary_format: BinaryFormat::Elf,
             architecture: to_object_architecture(arch)?,
-            endianness: Endianness::Little,
+            endianness: match arch.endianness().unwrap() {
+                target_lexicon::Endianness::Little => object::Endianness::Little,
+                target_lexicon::Endianness::Big => object::Endianness::Big,
+            },
         })
     }