Add *.o and *.a to .gitignore

Executables files should never make it into the repository anyway
and they pollute the output of other commands.

Change-Id: I07c1f927b45b771403965f7e0d545308532938d4
diff --git a/.gitignore b/.gitignore
index d2f549e..10831a2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,8 @@
 *.elf
 *.exe
 *.so
+*.o
+*.a
 
 # android: java build system
 /android/bin