internal/rosa/gnu: fetch mpc source via git

Eliminates the xz dependency.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/gnu.go

@@ -1141,15 +1141,22 @@ func init() {
 func (t Toolchain) newMPC() (pkg.Artifact, string) {
 	const (
 		version  = "1.4.0"
-		checksum = "75Sgr2hcDTltHYgFaHsRGsFgW74i2jqAUS0oXaBdJYKjMj_CvEeJ1zwGbNYjEl1H"
+		checksum = "TbrxLiE3ipQrHz_F3Xzz4zqBAnkMWyjhNwIK6wh9360RZ39xMt8rxfW3LxA9SnvU"
 	)
-	return t.NewPackage("mpc", version, pkg.NewHTTPGet(
-		nil, "https://ftpmirror.gnu.org/gnu/mpc/mpc-"+version+".tar.xz",
+	return t.NewPackage("mpc", version, t.NewViaGit(
+		"https://gitlab.inria.fr/mpc/mpc.git",
+		"refs/tags/"+version,
 		mustDecode(checksum),
 	), &PackageAttr{
-		SourceKind: SourceKindTarXZ,
-	}, (*MakeHelper)(nil),
-		XZ,
+		// does not find mpc-impl.h otherwise
+		EnterSource: true,
+	}, &MakeHelper{
+		InPlace:  true,
+		Generate: "autoreconf -vfi",
+	},
+		Automake,
+		Libtool,
+		Texinfo,
 
 		MPFR,
 	), version