Add merge-abi-diff to merge abi diff reports.

Bug: 38325929

Test: prebuilts/build-tools/build_prebuilts.sh succeeds.

Change-Id: I5523dd99169d6de5c4b48e2674a82247a84e2fc2
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index 4648db0..e39f6bd 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -39,7 +39,7 @@
 }
 EOF
     BUILDDIR=${SOONG_OUT} ./bootstrap.bash
-    SOONG_BINARIES=( acp bpfmt ckati ckati_stamp_dump ijar makeparallel ninja ziptime header-abi-linker header-abi-dumper header-abi-diff)
+    SOONG_BINARIES=( acp bpfmt ckati ckati_stamp_dump ijar makeparallel ninja ziptime header-abi-linker header-abi-dumper header-abi-diff merge-abi-diff)
     SOONG_ASAN_BINARIES=( acp ckati ijar makeparallel ninja ziptime )
     ${SOONG_OUT}/soong ${SOONG_BINARIES[@]/#/${SOONG_HOST_OUT}/bin/} ${SOONG_HOST_OUT}/nativetest64/ninja_test/ninja_test
     ${SOONG_HOST_OUT}/nativetest64/ninja_test/ninja_test