Support genrules with multiple tools

To allow genrules with more than one tool, rename the tool property to
tools and make it an array, replace $tool with $(location <label>),
and use $() for other variables for consistency.

Bug: 31948427
Test: compare build.ninja
Change-Id: I8d53510ac081ae20835b3ab7dfee3d74c520ab4d
(cherry picked from commit 7d332965ea44f54ddeedc9b7fadcf2e5b3259f3a)
diff --git a/compiler/Android.bp b/compiler/Android.bp
index b2ed074..f1bf27e 100644
--- a/compiler/Android.bp
+++ b/compiler/Android.bp
@@ -204,7 +204,8 @@
 
 gensrcs {
     name: "art_compiler_operator_srcs",
-    cmd: "art/tools/generate-operator-out.py art/compiler $in > $out",
+    cmd: "$(location generate-operator-out.py) art/compiler $(in) > $(out)",
+    tool_files: ["generate-operator-out.py"],
     srcs: [
         "compiled_method.h",
         "dex/dex_to_dex_compiler.h",