[LLDB] Make internal shell the default for running LLDB lit tests. (llvm#156729)

This patch updates the lld lit test config to use the internal shell by
default. This has some performance advantages (~10-15%) and also
produces nicer failure output. It also updates the two LLDB tests to not
require shell (so that they run under the internal shell), after first
verifying that they run and pass using the internal shell; and it fixes
one test that was not passing under the internal shell.

Author: cmtice

lldb/test/Shell/Process/Optimization.test

@@ -1,5 +1,5 @@
 Test warnings.
-REQUIRES: shell, system-darwin
+REQUIRES: system-darwin
 RUN: %clang_host -O3 %S/Inputs/true.c -std=c99 -g -o %t.exe
 RUN: %lldb -o "b main" -o r -o q -b %t.exe 2>&1 | FileCheck %s
 

lldb/test/Shell/Process/UnsupportedLanguage.test

@@ -1,7 +1,5 @@
 Test unsupported language warning
 
-REQUIRES: shell
-
 RUN: %clang_host %S/Inputs/true.c -std=c99 -g -c -S -emit-llvm -o - \
 RUN:   | sed -e 's/DW_LANG_C99/DW_LANG_Mips_Assembler/g' >%t.ll
 RUN: %clang_host %t.ll -g -o %t.exe

lldb/test/Shell/SymbolFile/DWARF/dwo-missing-error.test

@@ -11,12 +11,12 @@
 # "a.out-dwo-missing-error.dwo".
 # RUN: rm -rf %t.compdir/
 # RUN: mkdir -p %t.compdir/a/b/
-# RUN: cd %t.compdir/a/b/
+# RUN: pushd %t.compdir/a/b/
 # RUN: %clang_host %S/Inputs/dwo-missing-error.c -glldb -gdwarf-5 \
 # RUN:     -gsplit-dwarf -fdebug-prefix-map=%t.compdir=. -o a.out
 # RUN: rm *.dwo
 # RUN: %lldb a.out -s %s -o exit 2>&1 | FileCheck %s 
-# RUN: cd -
+# RUN: popd
 
 # Test the error message with an absolute DW_AT_comp_dir and DW_AT_dwo_name.
 # RUN: rm -rf %t.compdir/

lldb/test/Shell/lit.cfg.py

@@ -21,7 +21,15 @@
 config.name = "lldb-shell"
 
 # testFormat: The test format to use to interpret tests.
-config.test_format = toolchain.ShTestLldb(not llvm_config.use_lit_shell)
+# We prefer the lit internal shell which provides a better user experience on
+# failures and is faster unless the user explicitly disables it with
+# LIT_USE_INTERNAL_SHELL=0 env var.
+use_lit_shell = True
+lit_shell_env = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if lit_shell_env:
+    use_lit_shell = lit.util.pythonize_bool(lit_shell_env)
+
+config.test_format = toolchain.ShTestLldb(not use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files. This is overriden
 # by individual lit.local.cfg files in the test subdirectories.