Set Clang coverage environment variables.

Bug: 143977934
Bug: 161762585
Test: m CLANG_COVERAGE=true and check LLVM_PROFILE_FILE is set
Merged-In: I5aea5a38b9bec1670bf9c8d11d9c466c3b83e4d8
Change-Id: I5aea5a38b9bec1670bf9c8d11d9c466c3b83e4d8
(cherry picked from commit c1f7035c319aa51fa60d0e038e1bbbb41ac588ea)
2 files changed