[llvm-lit][test] Precommit tests for curly braces in lit internal shell

This patch creates tests to check lit's failure to execute curly braces
{}.

Author: connieyzhu

llvm/utils/lit/tests/Inputs/shtest-shell/curly-brace.txt

@@ -0,0 +1,12 @@
+## Test curly braces used in grouping commands.
+
+## Test one command inside curly brace.
+# RUN: { echo bar; } | FileCheck --check-prefix=ONE-CMD
+
+# ONE-CMD: bar
+
+## Test two commands inside curly brace.
+# RUN: { echo foo; echo bar; } | FileCheck --check-prefix=TWO-CMDS
+
+# TWO-CMDS: foo
+# TWO-CMDS: bar

llvm/utils/lit/tests/shtest-shell.py

@@ -44,6 +44,12 @@
 
 # CHECK: PASS: shtest-shell :: continuations.txt
 
+# CHECK: FAIL: shtest-shell :: curly-brace.txt
+# CHECK: # executed command: '{' echo bar
+# CHECK-NEXT: # .---command stderr------------
+# CHECK-NEXT: # | '{': command not found
+# CHECK: error: command failed with exit status: 127
+
 # CHECK: PASS: shtest-shell :: dev-null.txt
 
 #      CHECK: FAIL: shtest-shell :: diff-b.txt
@@ -651,4 +657,4 @@
 
 # CHECK: PASS: shtest-shell :: valid-shell.txt
 # CHECK: Unresolved Tests (1)
-# CHECK: Failed Tests (38)
+# CHECK: Failed Tests (39)