gdb/compile: Use std::filesystem::remove_all in cleanup

gdb/compile: Use std::filesystem::remove_all in cleanup

In a previous review, I noticed that some code in gdb/compile/compile.c
could use c++17's `std::filesystem::remove_all` instead of using some
`system ("rm -rf ...");`.

This patch implements this.

Note that I use the noexcept overload of std::filesystem::remove_all and
explicitly check for an error code.  This means that this code called
during the cleanup procedure cannot throw, and does not risk preventing
other cleanup functions to be called.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31420
Change-Id: If5668bf3e15e66c020e5c3b4fa999f861690e4cf
Approved-By: Tom Tromey <tom@tromey.com>