Do not add non-existing -Bprebuilts/gcc/.../bin

* Only prebuilts/gcc/linux-x86/host/x86_64-w64-mingw32-4.8/x86_64-w64-mingw32/bin
  exists for x86_windows_host.
* Remove config.ToolPath;
  add required -B flags into ToolchainCflags and ToolchainLdflags.

Bug: 218883919
Test: make droid tidy-soong_subset
Change-Id: I9a18bf8cc0cf84e091c7463b3bda316eaab53aa3
diff --git a/cc/compiler.go b/cc/compiler.go
index 9dbf2d1..d9a6bcd 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -450,11 +450,9 @@
 		}
 	}
 
-	gccPrefix := "-B" + config.ToolPath(tc)
-
-	flags.Global.CFlags = append(flags.Global.CFlags, target, gccPrefix)
-	flags.Global.AsFlags = append(flags.Global.AsFlags, target, gccPrefix)
-	flags.Global.LdFlags = append(flags.Global.LdFlags, target, gccPrefix)
+	flags.Global.CFlags = append(flags.Global.CFlags, target)
+	flags.Global.AsFlags = append(flags.Global.AsFlags, target)
+	flags.Global.LdFlags = append(flags.Global.LdFlags, target)
 
 	hod := "Host"
 	if ctx.Os().Class == android.Device {