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/config/x86_windows_host.go b/cc/config/x86_windows_host.go
index 9daf40f..2c83211 100644
--- a/cc/config/x86_windows_host.go
+++ b/cc/config/x86_windows_host.go
@@ -15,6 +15,7 @@
 package config
 
 import (
+	"path/filepath"
 	"strings"
 
 	"android/soong/android"
@@ -180,6 +181,14 @@
 	return "${config.WindowsGccTriple}"
 }
 
+func (t *toolchainWindows) ToolchainCflags() string {
+	return "-B" + filepath.Join(t.GccRoot(), t.GccTriple(), "bin")
+}
+
+func (t *toolchainWindows) ToolchainLdflags() string {
+	return "-B" + filepath.Join(t.GccRoot(), t.GccTriple(), "bin")
+}
+
 func (t *toolchainWindows) GccVersion() string {
 	return windowsGccVersion
 }