Do not set empty flags in build_llvm()

Bug: http://b/28196329

This code unnecssarily complicates configuring compiler and linker flags
from higher up in the call chain.  We can bring it back in the future if
we want to configure flags in this function specifically.

Change-Id: Ic22c3a5f07985d4818d2334f64c82587bcb973ea
1 file changed