Error compiling `build.sc`

**Type of issue**: bug report

**Impact**: unknown

~**Development Phase**: request | proposal~

~**Other information**~

**What is the current behavior?**

```bash
$ cd emulator/
$ make
cd /home/***/RISC-V/rocket-chip && mill rocketchip.assembly
Compiling /home/***/RISC-V/rocket-chip/build.sc
build.sc:594: not found: value Cross
trait JTAGDTMTest extends Cross.Module5[String, String, String, String, String] {
^
build.sc:468: not found: value Cross
trait ArchTest extends Cross.Module4[String, String, String, String] {
^
build.sc:440: not found: value Cross
trait RiscvTest extends Cross.Module4[String, String, String, String] {
^
build.sc:113: not found: value Cross
trait Emulator extends Cross.Module2[String, String] {
^
build.sc:68: not found: value millbuild
extends millbuild.common.RocketChipModule
^
build.sc:71: not found: value Cross
with Cross.Module[String] {
^
build.sc:56: not found: value millbuild
extends millbuild.cde.common.CDEModule
^
build.sc:36: not found: value millbuild
extends millbuild.hardfloat.common.HardfloatModule
^
build.sc:38: not found: value Cross
with Cross.Module[String] {
^
build.sc:24: not found: value millbuild
extends millbuild.common.MacrosModule
^
build.sc:426: not found: value Cross
trait Suite extends Cross.Module[String] {
^
build.sc:433: T{} members must be defs defined in a Cacher class/trait/object body
def binaries = T {
^
build.sc:429: T{} members must be defs defined in a Cacher class/trait/object body
def description = T {
^
build.sc:252: object Jvm is not a member of package mill.util
mill.util.Jvm.runSubprocess(Seq("cmake", "-G", "Ninja", "-S", cmakefileLists().path, "-B", T.dest.toString).map(_.toString), Map[String, String](), T.dest)
^
build.sc:120: object Jvm is not a member of package mill.util
mill.util.Jvm.javaExe,
^
build.sc:253: object Jvm is not a member of package mill.util
mill.util.Jvm.runSubprocess(Seq("ninja", "-C", T.dest).map(_.toString), Map[String, String](), T.dest)
^
build.sc:474: T{} members must be defs defined in a Cacher class/trait/object body
def ispecString = T {
^
build.sc:486: T{} members must be defs defined in a Cacher class/trait/object body
def pspecString = T {
^
build.sc:502: T{} members must be defs defined in a Cacher class/trait/object body
def spikeRoot = T {
^
build.sc:506: T{} members must be defs defined in a Cacher class/trait/object body
def CC = T {
^
build.sc:86: not found: value crossValue
def hardfloatModule = hardfloat(crossValue)
^
build.sc:82: not found: value crossValue
def chiselPluginIvy = Some(v.chiselCrossVersions(crossValue)._2)
^
build.sc:80: not found: value crossValue
def chiselIvy = Some(v.chiselCrossVersions(crossValue)._1)
^
build.sc:50: not found: value crossValue
def chiselPluginIvy = Some(v.chiselCrossVersions(crossValue)._2)
^
build.sc:48: not found: value crossValue
def chiselIvy = Some(v.chiselCrossVersions(crossValue)._1)
^
build.sc:48: `T.command` definitions must have 1 parameter list
def chiselIvy = Some(v.chiselCrossVersions(crossValue)._1)
^
build.sc:114: not found: value crossValue
val top: String = crossValue
^
build.sc:115: not found: value crossValue2
val config: String = crossValue2
^
build.sc:427: not found: value crossValue
val name: String = crossValue
^
build.sc:441: not found: value crossValue
val top: String = crossValue
^
build.sc:442: not found: value crossValue2
val config: String = crossValue2
^
build.sc:443: not found: value crossValue3
val suiteName: String = crossValue3
^
build.sc:444: not found: value crossValue4
val exclude: String = crossValue4
^
build.sc:469: not found: value crossValue
val top: String = crossValue
^
build.sc:470: not found: value crossValue2
val config: String = crossValue2
^
build.sc:471: not found: value crossValue3
val xlen: String = crossValue3
^
build.sc:472: not found: value crossValue4
val isa: String = crossValue4
^
build.sc:595: not found: value crossValue
val top: String = crossValue
^
build.sc:596: not found: value crossValue2
val config: String = crossValue2
^
build.sc:597: not found: value crossValue3
val sba: String = crossValue3
^
build.sc:598: not found: value crossValue4
val xlen: String = crossValue4
^
build.sc:599: not found: value crossValue5
val name: String = crossValue5
^
Compilation Failed
make: *** [/home/***/RISC-V/rocket-chip/Makefrag:47: /home/***/RISC-V/rocket-chip/out/rocketchip/assembly.dest/out.jar] Error 1
```

~**What is the expected behavior?**~

**Please tell us about your environment:**

- version: 50adbdb3e
- OS: `Linux bea1e-OptiPlex-5000 5.15.0-83-generic #92~20.04.1-Ubuntu SMP Mon Aug 21 14:00:49 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux`

~**What is the use case for changing the behavior?**~

Start by reproducing `cd emulator/` followed by `make` and inspect `build.sc`, especially the reported `Cross`, `millbuild`, `mill.util.Jvm`, and `crossValue` errors. Check `Makefrag` at the failing build target and compare the repository commit `50adbdb3e` with the expected build-tool setup. Done means the reported build completes without these compilation errors.

Written by the indexing model from the issue text.