Reland "Export prebuilt tools to Make" am: de9f477d5b am: 6ce4d07054

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/1392885

Change-Id: I4d8146ba2be1c298ddca1bd8c2bd03a180972a99
diff --git a/Android.bp b/Android.bp
index ee4089c..910290a 100644
--- a/Android.bp
+++ b/Android.bp
@@ -11,6 +11,7 @@
 prebuilt_build_tool {
     name: "bison",
     deps: ["common/bison/**/*"],
+    export_to_make_var: "BISON",
     target: {
         darwin: {
             src: "darwin-x86/bin/bison",
@@ -25,6 +26,7 @@
 
 prebuilt_build_tool {
     name: "flex",
+    export_to_make_var: "LEX",
     target: {
         darwin: {
             src: "darwin-x86/bin/flex",
@@ -37,6 +39,7 @@
 
 prebuilt_build_tool {
     name: "m4",
+    export_to_make_var: "M4",
     target: {
         darwin: {
             src: "darwin-x86/bin/m4",