[lldb] Quietly source lit-lldb-init

[kastiglione]

Summary

Improve utility of FileCheck output when a shell test fails.

The conflict is from:

1. On failure, FileCheck prints 5 lines of context
2. Shell tests first source lit-lldb-init, having the effect of printing its contents

If a FileCheck failure happens at the beginning of the input, then the
context shown is the lit-lldb-init, as it's over 5 lines and is the first
thing printed. As the init contents are fairly static, and presumably
uninteresting to most test failures, it seems reasonable to not print it.

Unfortunately it's not possible to use the --source-quietly flag in the lldb
invocation, because it will quiet all other --source flags on the command
line, making many tests fail.

This fix is a level of indirection, where a new sibling file named
lit-lldb-init-quiet is created, and its static contents are:

command source -C --silent-run true lit-lldb-init

This achieves the result of loading lit-lldb-init quietly. The -C flag
loads the path relatively.

[JDevlieghere]

LGTM

lldb/test/Shell/CMakeLists.txt

 add_custom_target(lldb-shell-test-deps)
 add_dependencies(lldb-shell-test-deps lldb-test-depends)
 
 add_lit_testsuites(LLDB-SHELL
   ${CMAKE_CURRENT_SOURCE_DIR}
   DEPENDS lldb-shell-test-deps)
 
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
   MAIN_CONFIG
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py)
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit-lldb-init.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit-lldb-init)
 
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/lit-lldb-init-quiet
+  "command source -C --silent-run true lit-lldb-init\n")
+
 add_lit_testsuite(check-lldb-shell "Running lldb shell test suite"
   ${CMAKE_CURRENT_BINARY_DIR}
   EXCLUDE_FROM_CHECK_ALL
   DEPENDS lldb-shell-test-deps)

lldb/test/Shell/helper/toolchain.py

 import os
 import itertools
 import platform
 import subprocess
 import sys
 
 import lit.util
 from lit.llvm import llvm_config
 from lit.llvm.subst import FindTool
 from lit.llvm.subst import ToolSubst
 
 
 def _get_lldb_init_path(config):
-    return os.path.join(config.test_exec_root, 'lit-lldb-init')
+    return os.path.join(config.test_exec_root, 'lit-lldb-init-quiet')
 
 
 def _disallow(config, execName):
   warning = '''
     echo '*** Do not use \'{0}\' in tests; use \'%''{0}\'. ***' &&
     exit 1 && echo
   '''
   config.substitutions.append((' {0} '.format(execName),