fix(bootstrap): resolve lir lower crashes and struct-copy bugs

- Fix lirValToC crash on lvkInt in hStore raw C emission
- Add hAlloca handling to lowerExpr (returns &name, avoids unhandled fallback)
- Fix nested comment syntax in unhandled expr fallback
- Rewrite buildLval to handle hIndexPtr and nested hFieldPtr/hArrowField
  so assignments like arr[i].field = val emit direct C lvalues
- Make &&/|| temporaries unique (__and_tmp_N/__or_tmp_N) to avoid
  duplicate declarations in the same function
- Selfhost null-deref fix in sema.bux (unchained nested conditions)

bootstrap/cli.nim

@@ -488,7 +488,7 @@ proc cmdBuild*(args: seq[string], opts: GlobalOptions): int =
   # Compile with cc
   let outputName = if pctx.man.name != "": pctx.man.name else: "bux_out"
   let outputFile = buildDir / outputName
-  let ccCmd = &"cc -O2 -pthread -o {outputFile} {cFile} {runtimeDst} {ioDst} -lm -lcrypto 2>&1"
+  let ccCmd = &"cc -O0 -g -pthread -o {outputFile} {cFile} {runtimeDst} {ioDst} -lm -lcrypto 2>&1"
   if opts.verbose:
     printInfo(&"running: {ccCmd}", useColor)
   let (output, exitCode) = execCmdEx(ccCmd)