Add gomacc.lock and make files generated by gyp into .gitignore

Change-Id: I8e0ca43badd9a66586e7a18985f26fb46a9e02e3
Reviewed-on: https://weave-review.googlesource.com/1630
Reviewed-by: Vitaly Buka <vitalybuka@google.com>

.gitignore

diff --git a/.gitignore b/.gitignore
index 4011af4..3ee16a1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,7 @@
+*.target.mk
 *~
 /out/
 /third_party/include
 /third_party/lib
+gomacc.lock
+Makefile