[LLDB] Make internal shell the default for running LLDB lit tests.

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.