[gdb/symtab] Trust epilogue unwind info for unknown or non-gcc producer

Currently we only trust epilogue unwind info only for gcc >= 4.5.0.

This has the effect that we don't trust epilogue unwind info for:
- unknown producers (CU without DW_AT_producer attribute)
- non-gcc producers (say, clang).

Instead, only distrust epilogue unwind info only for gcc < 4.5.0.
1 file changed