Add GDB pretty-printer for thrust vectors and references

[upsj]

I saw #1318 and really liked the idea of providing pretty-printers even for device-side data, so I implemented it in our own library (ginkgo-project/ginkgo#987), and thought it might be useful here as well :) I removed all non-trivial parts of the code that were copied from libstdc++, so there should be no licensing issues. This is should be straightforward to extend to device references , I only had a few issues with getting the device pointer out from a device_reference (gdb returns a heap pointer for D[0].ptr.m_iterator, but what looks like a device pointer for D.m_storage.m_begin.m_iterator.m_iterator in examples/basic_vector.cu, so there must be something weird going wrong with the temporary D[0] I guess?)

I can't really speak on the potential for hangs that was discussed in the original issue, aside from "it works for me" - that would be something the runtime folks need to answer.

Example run:

(gdb) b 33
Breakpoint 1 at 0xc3e8: file /home/tobi/thrust/examples/basic_vector.cu, line 33.
(gdb) run
Starting program: /home/tobi/thrust/build/bin/thrust.example.basic_vector 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
H has size 4
H[0] = 14
H[1] = 20
H[2] = 38
H[3] = 46
H now has size 2
[New Thread 0x7fffefea3000 (LWP 2198)]

Thread 1 "thrust.example." hit Breakpoint 1, main () at /home/tobi/thrust/examples/basic_vector.cu:33
33          D[0] = 99;
(gdb) source ../scripts/gdb-pretty-printers.py 
(gdb) print H
$1 = thrust::host_vector<int, std::allocator<int> > of length 2, capacity 4 = {14, 20}
(gdb) print D
$2 = thrust::device_vector<int, thrust::device_allocator<int> > of length 2, capacity 2 = {14, 20}
(gdb) print D[1]
$3 = (thrust::device_reference<int>) @0xb047f0004: 20
(gdb)

Fixes #1318

[alliepiper]

Awesome, thanks! We'll take a look soon, but it may be sometime after GTC.

[GPUtester]

Can one of the admins verify this patch?

[upsj]

I figured out the issues with device references, turns out GDB <= 9.2 has some bug I didn't bother to track down that has been fixed in GDB 10.1, so we can actually conditionally add pretty printers for references as well :)

[ericniebler]

Looks good to me. Thanks!