Motivation example:
```
> lldb -c altmain2.core
...
(lldb) var F
(const char *) F = 0x0804a000 ""
```
The variable `F` points to a read-only memory page not dumped to the
core file, so `Process::ReadMemory()` cannot read the data. The patch
switches to `Target::ReadMemory()`, which can read data both from the
process memory and the application binary.
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