Avoid writing to source dir while building guice

One of the external/guice build rules uses zip. By default zip
will create a temporary working directory next to the source archive.

Instead of tainting the source directory let's make it use
the standard /tmp directory.

Test: make checkbuild dist tests
Change-Id: I99ad49f12923be3a81f10f511091d8485f74c596
diff --git a/Android.bp b/Android.bp
index 1cd42f3..57f5e1c 100644
--- a/Android.bp
+++ b/Android.bp
@@ -58,7 +58,7 @@
     name: "guice_munge_srcjar",
     out: ["guice_munge.srcjar"],
     srcs: ["lib/build/munge.jar"],
-    cmd: "zip $(in) -O $(out) -d MungeTask.java",
+    cmd: "zip --temp-path $${TMPDIR:-/tmp} $(in) -O $(out) -d MungeTask.java",
 }
 
 genrule {