builder: simplify bdwgc libc dependency

Header files are built immediately, not in a separate job, so no
dependency is needed here. All we need is a flag whether to add flags
for that given libc.

builder/bdwgc.go

@@ -49,6 +49,7 @@ var BoehmGC = Library{
 			"-I" + libdir + "/include",
 		}
 	},
+	needsLibc: true,
 	sourceDir: func() string {
 		return filepath.Join(goenv.Get("TINYGOROOT"), "lib/bdwgc")
 	},

builder/build.go

@@ -147,14 +147,13 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	// the libc needs them.
 	root := goenv.Get("TINYGOROOT")
 	var libcDependencies []*compileJob
-	var libcJob *compileJob
 	switch config.Target.Libc {
 	case "darwin-libSystem":
-		libcJob = makeDarwinLibSystemJob(config, tmpdir)
+		libcJob := makeDarwinLibSystemJob(config, tmpdir)
 		libcDependencies = append(libcDependencies, libcJob)
 	case "musl":
 		var unlock func()
-		libcJob, unlock, err = libMusl.load(config, tmpdir, nil)
+		libcJob, unlock, err := libMusl.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}
@@ -162,7 +161,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		libcDependencies = append(libcDependencies, dummyCompileJob(filepath.Join(filepath.Dir(libcJob.result), "crt1.o")))
 		libcDependencies = append(libcDependencies, libcJob)
 	case "picolibc":
-		libcJob, unlock, err := libPicolibc.load(config, tmpdir, nil)
+		libcJob, unlock, err := libPicolibc.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}
@@ -175,15 +174,14 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		}
 		libcDependencies = append(libcDependencies, dummyCompileJob(path))
 	case "wasmbuiltins":
-		libcJob, unlock, err := libWasmBuiltins.load(config, tmpdir, nil)
+		libcJob, unlock, err := libWasmBuiltins.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}
 		defer unlock()
 		libcDependencies = append(libcDependencies, libcJob)
 	case "mingw-w64":
-		var unlock func()
-		libcJob, unlock, err = libMinGW.load(config, tmpdir, nil)
+		libcJob, unlock, err := libMinGW.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}
@@ -704,7 +702,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	// Add compiler-rt dependency if needed. Usually this is a simple load from
 	// a cache.
 	if config.Target.RTLib == "compiler-rt" {
-		job, unlock, err := libCompilerRT.load(config, tmpdir, nil)
+		job, unlock, err := libCompilerRT.load(config, tmpdir)
 		if err != nil {
 			return result, err
 		}
@@ -714,10 +712,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 
 	// The Boehm collector is stored in a separate C library.
 	if config.GC() == "boehm" {
-		if libcJob == nil {
-			return BuildResult{}, fmt.Errorf("boehm GC isn't supported with libc %s", config.Target.Libc)
-		}
-		job, unlock, err := BoehmGC.load(config, tmpdir, libcJob)
+		job, unlock, err := BoehmGC.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}

builder/library.go

@@ -25,6 +25,9 @@ type Library struct {
 	// cflags returns the C flags specific to this library
 	cflags func(target, headerPath string) []string
 
+	// needsLibc is set to true if this library needs libc headers.
+	needsLibc bool
+
 	// The source directory.
 	sourceDir func() string
 
@@ -43,11 +46,7 @@ type Library struct {
 // output archive file, it is expected to be removed after use.
 // As a side effect, this call creates the library header files if they didn't
 // exist yet.
-// The provided libc job (if not null) will cause this libc to be added as a
-// dependency for all C compiler jobs, and adds libc headers for the given
-// target config. In other words, pass this libc if the library needs a libc to
-// compile.
-func (l *Library) load(config *compileopts.Config, tmpdir string, libc *compileJob) (job *compileJob, abortLock func(), err error) {
+func (l *Library) load(config *compileopts.Config, tmpdir string) (job *compileJob, abortLock func(), err error) {
 	outdir := config.LibcPath(l.name)
 	archiveFilePath := filepath.Join(outdir, "lib.a")
 
@@ -180,7 +179,7 @@ func (l *Library) load(config *compileopts.Config, tmpdir string, libc *compileJ
 			args = append(args, "-mfpu=vfpv2")
 		}
 	}
-	if libc != nil {
+	if l.needsLibc {
 		args = append(args, config.LibcCFlags()...)
 	}
 
@@ -251,9 +250,6 @@ func (l *Library) load(config *compileopts.Config, tmpdir string, libc *compileJ
 				return nil
 			},
 		}
-		if libc != nil {
-			objfile.dependencies = append(objfile.dependencies, libc)
-		}
 		job.dependencies = append(job.dependencies, objfile)
 	}
 
@@ -284,9 +280,6 @@ func (l *Library) load(config *compileopts.Config, tmpdir string, libc *compileJ
 				return os.Rename(tmpfile.Name(), filepath.Join(outdir, "crt1.o"))
 			},
 		}
-		if libc != nil {
-			crt1Job.dependencies = append(crt1Job.dependencies, libc)
-		}
 		job.dependencies = append(job.dependencies, crt1Job)
 	}