[gdb/corefiles] Sort info proc mappings table

[gdb/corefiles] Sort info proc mappings table

On x86_64-linux, with test-case gdb.python/py-corefile.exp I run into:
...
FAIL: $exp: test mapped files data: diff input and output one
...

The failing test compares the output of:
- info proc mappings, and
- info proc py-mappings, a python implementation of "info proc mappings".

The difference in output is order: while the latter prints the entries sorted
on start address, the former doesn't.

Fix this by sorting the entries in linux_read_core_file_mappings.

Tested on x86_64-linux.

PR corefiles/33543
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33543