[ProfileData] Propagate an error from InstrProfSymtab
[ProfileData] Propagate an error from InstrProfSymtab

CovMapFuncReader::get should propagate up errors from InstrProfSymtab.

This is part of a series of patches to transition ProfileData over to
the stricter Error/Expected interface.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@268428 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit f8e08351d31a188a327537eb2ffb696ee6d56ca7)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm