Changes

[MC] Emit unused undefined symbol even if its binding is not set
Recommit r373168, which was reverted by r373242. This actually exposed a 
boringssl bug which has been fixed for more than one month.
For the following two cases, we currently suppress the symbols. This 
patch emits them (compatible with GNU as).
* `test2_a = undef`: if `undef` is otherwise unused.
* `.hidden hidden`: if `hidden` is unused. This is the main point of the
 patch, because omitting the symbol would cause a linker semantic
 difference.
It causes a behavior change that is not compatible with GNU as:
.weakref foo1, bar1
When neither foo1 nor bar1 is used, we now emit bar1, which is arguably 
more consistent.
Another change is that we will emit .TOC. for .TOC.@tocbase .  For this 
directive, suppressing .TOC. can be seen as a size optimization, but we 
choose to drop it for simplicity and consistency.

[clangd] NFC, reuse the source manager variable in the RawStringLiteral
apply method
Differential Revision: https://reviews.llvm.org/D69544

Debug Info: Nest Objective-C property function decls inside their
container.
This has the nice side-effect of also fixing a crash in Clang.
Starting with DWARF 5 we are emitting ObjC method declarations as 
children of their containing entity. This worked for interfaces, but 
didn't consider the case of synthessized properties. When a property of
a protocol is synthesized in an interface implementation the 
ObjCMethodDecl that was passed to CGF::StartFunction was the property
*declaration* which obviously couldn't have a containing interface. This
patch passes the containing interface all the way through to
CGDebugInfo, so the function declaration can be created with the correct
parent (= the class implementing the protocol).
rdar://problem/53782400
Differential Revision: https://reviews.llvm.org/D66121

NVPTX: Don't insert an extra empty line at the end of the last section.
This was arbitrarily appearing in only the last section emitted - which 
made tests more sensitive than they needed to be (removing the last 
section - like the macinfo section change that's coming after this) 
would, surprisingly, move the blank line to the previous section.

llvm-ranlib/nm: Don't print usage message except for usage errors
Also, fix a bug in ranlib where it didn't correctly detect being run 
without any argument and would try to operate on the empty string.
Differential Revision: https://reviews.llvm.org/D70021

DebugInfo: Do not create a debug_macinfo section if no CUs have
associated macros
Patch based on Sourabh Singh's D69839 patch.

DebugInfo: Remove redundant conditionals/checks from macro info emission
These checks fall out naturally from the current implementation without 
needing to be explicitly considered anymore.

Test case to verify that lldb falls back to p/P if g is unsupported and
that lldb uses the expedited register values in the ? packet aka stop
packet (T11 etc) and does not re-fetch them with the p packet.
This test is currently failing from the "[lldb-server] Add setting to 
force 'g' packet use" commit; I'm marking it as @expectedFailureAll 
until we can get this fixed.