Bug#851371: libllvm3.9-dbg: lots of "Could not find DWO" and "in read in psymtab, but not in symtab" warnings

[Rebecca N. Palmer]

Control: severity -1 minor

(Found while investigating #852746 - these are the only two places in LLVM with 
that error message,

Oops - there are actually three and #852746 is the other one.  Sorry for noise.