Add aninja to envsetup.sh

Add an aninja function to envsetup.sh that can run ninja with the
appropriate ninja file for an Android build.  Simplifies running
queries with ninja.  For example:
aninja -t query droid

Test: aninja -t query droid
Change-Id: I7064984d55054cd4350800cfd75bf6aaa1740e9d

envsetup.sh

@@ -2059,6 +2059,11 @@ function overrideflags() {
     (\cd "${T}" && build/make/tools/overrideflags.sh "$@")
 }
 
+function aninja() {
+    local T="$(gettop)"
+    (\cd "${T}" && prebuilts/build-tools/linux-x86/bin/ninja -f out/combined-${TARGET_PRODUCT}.ninja "$@")
+}
+
 validate_current_shell
 set_global_paths
 source_vendorsetup