[asan] Support line numbers in StackVarDescr

When -fsanitize-address-use-after-scope is used, the instrumentation produces line numbers in stack frame descriptions. This patch make sure the ASan runtime supports this format (ParseFrameDescription needs to be able to parse "varname:line") and prepares lit tests to allow line numbers in ASan report output.

Differential Revision: https://reviews.llvm.org/D31484

llvm-svn: 299043