Split the x86 host toolchain into glibc and musl variants

Create new musl toolchains that are based on the existing glibc
toolchains, and add the necessary flags for musl compiles.

Bug: 190084016
Test: TestArchMutator
Change-Id: Ifc02f9e5afa61ff758be98b0c962f3a4b53d0546

android/paths.go

@@ -1667,7 +1667,7 @@ func pathForInstall(ctx PathContext, os OsType, arch ArchType, partition string,
 		partionPaths = []string{"target", "product", ctx.Config().DeviceName(), partition}
 	} else {
 		osName := os.String()
-		if os == Linux {
+		if os == Linux || os == LinuxMusl {
 			// instead of linux_glibc
 			osName = "linux"
 		}