start unittests for the system.c file

Not a lot here, but better than nothing!

Bug: None
Test: system_unittest passes
Change-Id: I33015ad2193bde8b09be82af65c106da2716262b
diff --git a/.gitignore b/.gitignore
index 248dbe5..a121c9e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,10 +8,11 @@
 *.so
 
 # Executables when compiling in-tree.
-libminijail_unittest
-minijail0
-syscall_filter_unittest
-parse_seccomp_policy
+/libminijail_unittest
+/minijail0
+/syscall_filter_unittest
+/system_unittest
+/parse_seccomp_policy
 
 # common.mk TEST().
 *.test