envsetup: export ANDROID_BUILD_TOP earlier

Change-Id: Ia3497f61f4e9aaeeb793cecd3b4f488f0a48181a
diff --git a/envsetup.sh b/envsetup.sh
index be6061d..f802573 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -359,7 +359,6 @@
     setpaths
     set_sequence_number
 
-    export ANDROID_BUILD_TOP=$(gettop)
     # With this environment variable new GCC can apply colors to warnings/errors
     export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'
 }
@@ -1963,3 +1962,5 @@
 validate_current_shell
 source_vendorsetup
 addcompletions
+
+export ANDROID_BUILD_TOP=$(gettop)