winch: Adding support for integration tests (#5588)

* Adding in the foundations for Winch `filetests`

This commit adds two new crates into the Winch workspace:
`filetests` and `test-macros`. The intent is to mimic the
structure of Cranelift `filetests`, but in a simpler way.

* Updates to documentation

This commits adds a high level document to outline how to test Winch
through the `winch-tools` utility. It also updates some inline
documentation which gets propagated to the CLI.

* Updating test-macro to use a glob instead of only a flat directory

winch/filetests/src/disasm.rs

@@ -0,0 +1,59 @@
+//! Disassembly utilities.
+
+use anyhow::{bail, Result};
+use capstone::prelude::*;
+use std::fmt::Write;
+use target_lexicon::Architecture;
+use winch_codegen::TargetIsa;
+
+/// Disassemble and print a machine code buffer.
+pub fn disasm(bytes: &[u8], isa: &dyn TargetIsa) -> Result<Vec<String>> {
+    let dis = disassembler_for(isa)?;
+    let insts = dis.disasm_all(bytes, 0x0).unwrap();
+
+    let disassembled_lines = insts
+        .iter()
+        .map(|i| {
+            let mut line = String::new();
+
+            write!(&mut line, "{:4x}:\t ", i.address()).unwrap();
+
+            let mut bytes_str = String::new();
+            let mut len = 0;
+            for b in i.bytes() {
+                write!(&mut bytes_str, "{:02x}", b).unwrap();
+                len += 1;
+            }
+            write!(&mut line, "{:21}\t", bytes_str).unwrap();
+            if len > 8 {
+                write!(&mut line, "\n\t\t\t\t").unwrap();
+            }
+
+            if let Some(s) = i.mnemonic() {
+                write!(&mut line, "{}\t", s).unwrap();
+            }
+
+            if let Some(s) = i.op_str() {
+                write!(&mut line, "{}", s).unwrap();
+            }
+
+            line
+        })
+        .collect();
+
+    Ok(disassembled_lines)
+}
+
+fn disassembler_for(isa: &dyn TargetIsa) -> Result<Capstone> {
+    let disasm = match isa.triple().architecture {
+        Architecture::X86_64 => Capstone::new()
+            .x86()
+            .mode(arch::x86::ArchMode::Mode64)
+            .build()
+            .map_err(|e| anyhow::format_err!("{}", e))?,
+
+        _ => bail!("Unsupported ISA"),
+    };
+
+    Ok(disasm)
+}