rustdoc: hide private traits in strip-private pass

Fix #16563
Fix issue #17848 (Questionable advice in bug report instructions)
Add test for issue #17594
debuginfo: Gate all LLDB debuginfo tests on a minimum LLDB version being available
debuginfo: Make some path LLDB-related paths in the test runner absolute to help the build bots.
debuginfo: Enable LLDB test suite on Darwin.
debuginfo: Let LLDB tests run in parallel again since our min-supported version has no problems with that.
debuginfo: Print more output in lldb_batchmode.py for better error logs.
auto merge of #17846 : tomjakubowski/rust/rustdoc-hide-private-traits, r=alexcrichton

Fix #16563
auto merge of #18092 : michaelwoerister/rust/lldb-test-versioning, r=alexcrichton

Now that there are build bots with a stable enough LLDB version on OSX we can finally let the tests run on every PR!
:joy_cat:
auto merge of #18224 : nikomatsakis/rust/issue-17594, r=alexcrichton

Add test for issue #17594

Fixes #17594
Add run-pass-valgrind tests

Closes #16914
Move some tests to run-pass-valgrind
Make rpass-valgrind work with pretty
Remove support for .rc files from test.mk
Error if we should be able to Valgrind but can't
auto merge of #17868 : nick29581/rust/valgrind, r=alexcrichton

r? @alexcrichton
auto merge of #18217 : mikedilger/rust/bug_report_instructions, r=pnkfelix

Fixed as per @pnkfelix comments in #17848