llvm-symbolizer: fix handling of DW_AT_specification in FRAME.
Summary:
Use getSubroutineName() to the the subrouting name; this function knows
how to handle cases when DW_TAG_subprogram refers to an earlier
declaration:
0x00000050: DW_TAG_subprogram
DW_AT_linkage_name ("_ZN1A1fEv")
DW_AT_name ("f")
...
0x00000067: DW_TAG_subprogram
DW_AT_low_pc (0x0000000000000000)
DW_AT_high_pc (0x0000000000000020)
DW_AT_specification (0x00000050 "_ZN1A1fEv")
...
0x0000008c: DW_TAG_variable
Reviewers: pcc, vitalybuka, jdoerfert
Subscribers: srhines, hiraditya, rupprecht, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70630