[BoundsSafety][LLDB] Implement instrumentation plugin for -fbounds-safety soft traps

This patch tries to upstream code landed downstream in
swiftlang#11835.

This patch implements an instrumentation plugin for the
`-fbounds-safety` soft trap mode first implemented in
swiftlang#11645 (rdar://158088757).
That functionality isn't supported in upstream Clang yet, however the
instrumented plugin can be compiled without issue so this patch tries to
upstream it. The included tests are all disabled when the clang used for
testing doesn't support `-fbounds-safety`. This means the tests will be
skipped. However, it's fairly easy to point LLDB at a clang that does
support `-fbounds-safety. I've done this and confirmed the tests pass.
To use a custom clang the following can be done:

* For API tests set the `LLDB_TEST_COMPILER` CMake cache variable to
  point to appropriate compiler.
* For shell tests applying a patch like this can be used to set the
  appropriate compiler:

```
--- a/lldb/test/Shell/helper/toolchain.py
+++ b/lldb/test/Shell/helper/toolchain.py
@@ -271,6 +271,7 @@ def use_support_substitutions(config):
     if config.lldb_lit_tools_dir:
         additional_tool_dirs.append(config.lldb_lit_tools_dir)

+    config.environment['CLANG'] = '/path/to/clang'
     llvm_config.use_clang(
```

The current implementation of -fbounds-safety traps works by emitting
calls to runtime functions intended to log the occurrence of a soft trap.
While the user could just set a breakpoint of these functions the
instrumentation plugin sets it automatically and provides several
additional features:

When debug info is available:

* It adjusts the stop reason to be the reason for trapping. This is
  extracted from the artificial frame in the debug info (similar to
  -fbounds-safety hard traps).
* It adjusts the selected frame to be the frame where the soft trap
  occurred.

When debug info is not available:

* For the `call-with-str` soft trap mode the soft trap reason is
  read from the first argument register.
* For the `call-minimal` soft trap mode the stop reason is adjusted
  to note its a bounds check failure but does not give further
  information because none is available.
* In this situation the selected frame is not adjusted because in
  this mode the user will be looking at assembly and adjusting the
  frame makes things confusing.

This patch includes shell and api tests. The shell tests seemed like the
best way to test behavior when debug info is missing because those tests
make it easy to disable building with debug info completely.

rdar://163230807

Author: delcypher

lldb/include/lldb/lldb-enumerations.h

@@ -542,6 +542,7 @@ enum InstrumentationRuntimeType {
   eInstrumentationRuntimeTypeMainThreadChecker = 0x0003,
   eInstrumentationRuntimeTypeSwiftRuntimeReporting = 0x0004,
   eInstrumentationRuntimeTypeLibsanitizersAsan = 0x0005,
+  eInstrumentationRuntimeTypeBoundsSafety = 0x0006,
   eNumInstrumentationRuntimeTypes
 };
 

lldb/source/Plugins/InstrumentationRuntime/BoundsSafety/CMakeLists.txt

@@ -0,0 +1,13 @@
+add_lldb_library(lldbPluginInstrumentationRuntimeBoundsSafety PLUGIN
+  InstrumentationRuntimeBoundsSafety.cpp
+
+  LINK_LIBS
+    lldbBreakpoint
+    lldbCore
+    lldbSymbol
+    lldbTarget
+    lldbPluginInstrumentationRuntimeUtility
+
+  CLANG_LIBS
+    clangCodeGen
+  )