odrefresh: Avoid uninitialized usage

compilation_os_mode_ was only getting set when
SetCompilationOsMode() was called.  We initialize it to make sure
we have a consistent value if that function isn't called.

Test: TreeHugger
Bug: 211458160
Change-Id: Ic743969d3d0153561211a69eb32d5509e1c83cca
1 file changed