Support running soong_ui.bash from anywhere in the tree

It will cd to $TOP before running soong_ui itself, so that soong_ui
still runs from the top of the tree. ORIGINAL_PWD is saved so that we
can reference that later (for example, to move 'mma' implementation into
Go).

Test: cd system; ../build/soong/soong_ui.bash
Test: Set absolute / relative OUT_DIR or OUT_DIR_COMMON_BASE and repeat
Change-Id: Icb67a3ee6a3358cca50300755c8953419fc19437

cmd/microfactory/microfactory.bash

@@ -39,9 +39,12 @@ function getoutdir
         if [ "${OUT_DIR_COMMON_BASE-}" ]; then
             out_dir="${OUT_DIR_COMMON_BASE}/$(basename ${TOP})"
         else
-            out_dir="${TOP}/out"
+            out_dir="out"
         fi
     fi
+    if [[ "${out_dir}" != /* ]]; then
+        out_dir="${TOP}/${out_dir}"
+    fi
     echo "${out_dir}"
 }
 

soong_ui.bash

@@ -47,8 +47,12 @@ function gettop
     fi
 }
 
+# Save the current PWD for use in soong_ui
+export ORIGINAL_PWD=${PWD}
 export TOP=$(gettop)
-source build/soong/cmd/microfactory/microfactory.bash
+source ${TOP}/build/soong/cmd/microfactory/microfactory.bash
 
 build_go soong_ui android/soong/cmd/soong_ui
+
+cd ${TOP}
 exec "$(getoutdir)/soong_ui" "$@"