debug: Support big-endian architectures

This fixes some hard-coded assumptions in the debug crate that
the native ELF files being accessed are little-endian; specifically
in create_gdbjit_image as well as in emit_dwarf.

In addition, data in WebAssembly memory always uses little-endian
byte order.  Therefore, if the native architecture is big-endian,
all references to base types need to be marked as little-endian
using the DW_AT_endianity attribute, so that the debugger will
be able to correctly access them.

crates/environ/src/data_structures.rs

@@ -3,8 +3,8 @@
 pub mod ir {
     pub use cranelift_codegen::binemit::{Reloc, StackMap};
     pub use cranelift_codegen::ir::{
-        types, AbiParam, ArgumentPurpose, JumpTableOffsets, LabelValueLoc, LibCall, Signature,
-        SourceLoc, StackSlots, TrapCode, Type, ValueLabel, ValueLoc,
+        types, AbiParam, ArgumentPurpose, Endianness, JumpTableOffsets, LabelValueLoc, LibCall,
+        Signature, SourceLoc, StackSlots, TrapCode, Type, ValueLabel, ValueLoc,
     };
     pub use cranelift_codegen::{ValueLabelsRanges, ValueLocRange};
 }