Define ANDROID_EXPERIMENTAL_MTE if the product variable experimental_mte is enabled.

This will activate code in bionic that uses the experimental MTE
userspace interface.

Bug: 135772972
Change-Id: I9ac641b9528de5376cdb920bee0e900a1b1fa9c2
diff --git a/libc/Android.bp b/libc/Android.bp
index ae943fc..53a26a6 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -83,6 +83,12 @@
     // lld complains about duplicate symbols in libcrt and libgcc. Suppress the
     // warning since this is intended right now.
     ldflags: ["-Wl,-z,muldefs"],
+
+    product_variables: {
+        experimental_mte: {
+            cflags: ["-DANDROID_EXPERIMENTAL_MTE"],
+        },
+    },
 }
 
 // Defaults for native allocator libs/includes to make it