[lldb] Add asan flags to TestCustomShell

As discussed in 9785749, we need to
disable "user poisoning" in swift's fork of llvm. However, this
particular test overrides the environment, so we need to propagate the
asan flags manually.

(cherry picked from commit cfe2542)

Author: felipepiovezan

lldb/test/Shell/Host/TestCustomShell.test

@@ -7,7 +7,7 @@
 
 # RUN: %clang_host %S/Inputs/simple.c -g -o %t.out
 # RUN: SHELL=bogus not %lldb %t.out -b -o 'process launch -X 1 --' 2>&1 | FileCheck %s --check-prefix ERROR
-# RUN: env -i ASAN_OPTIONS='detect_container_overflow=0' %lldb %t.out -b -o 'process launch -X 1 --' 2>&1 | FileCheck %s
+# RUN: env -i ASAN_OPTIONS='detect_container_overflow=0,allow_user_poisoning=0' %lldb %t.out -b -o 'process launch -X 1 --' 2>&1 | FileCheck %s
 
 # ERROR: error: shell expansion failed
 # CHECK-NOT: error: shell expansion failed