Fix upper->lower case for /usr/lib/debug/.build-id/**.debug

I have found the lookup by build-id
(when lookup by /usr/lib/debug/path/name/exec.debug failed) does not work as
LLDB tries the build-id hex string in uppercase but Fedora uses lowercase.

xubuntu-16.10 also uses lowercase during my test:
/usr/lib/debug/.build-id/6c/61f3566329f43d03f812ae7057e9e7391b5ff6.debug

Differential revision: https://reviews.llvm.org/D42852

llvm-svn: 324222