Fix test failure on non-darwin bots

[rastogishubham]

The test still fails on non-Darwin bots, for example:

https://ci.swift.org/job/oss-swift-package-amazon-linux-2-aarch64

RUN: at line 1: /home/build-user/build/buildbot_linux/swift-linux-aarch64/bin/sil-opt -target aarch64-unknown-linux-gnu  -module-cache-path /home/build-user/build/buildbot_linux/swift-linux-aarch64/swift-test-results/aarch64-unknown-linux-gnu/clang-module-cache  --diagnose-unreachable -o - /home/build-user/swift/test/DebugInfo/dropped-var.sil -sil-stats-lost-variables --target=aarch64-apple-darwin 2>&1 | /usr/bin/python3.7 /home/build-user/swift/utils/PathSanitizingFileCheck --allow-unused-prefixes --sanitize BUILD_DIR=/home/build-user/build/buildbot_linux/swift-linux-aarch64 --sanitize SOURCE_DIR=/home/build-user/swift --use-filecheck /home/build-user/build/buildbot_linux/llvm-linux-aarch64/bin/FileCheck   /home/build-user/swift/test/DebugInfo/dropped-var.sil
+ /usr/bin/python3.7 /home/build-user/swift/utils/PathSanitizingFileCheck --allow-unused-prefixes --sanitize BUILD_DIR=/home/build-user/build/buildbot_linux/swift-linux-aarch64 --sanitize SOURCE_DIR=/home/build-user/swift --use-filecheck /home/build-user/build/buildbot_linux/llvm-linux-aarch64/bin/FileCheck /home/build-user/swift/test/DebugInfo/dropped-var.sil
+ /home/build-user/build/buildbot_linux/swift-linux-aarch64/bin/sil-opt -target aarch64-unknown-linux-gnu -module-cache-path /home/build-user/build/buildbot_linux/swift-linux-aarch64/swift-test-results/aarch64-unknown-linux-gnu/clang-module-cache --diagnose-unreachable -o - /home/build-user/swift/test/DebugInfo/dropped-var.sil -sil-stats-lost-variables --target=aarch64-apple-darwin
/home/build-user/swift/test/DebugInfo/dropped-var.sil:4:12: error: CHECK: expected string not found in input
 // CHECK: function, lostvars, Pass List Pipeline, DiagnoseUnreachable, 1, 1, {{[0-9]+}}, $s4test3bar1yS2i_tF
           ^
<stdin>:1:1: note: scanning from here
SOURCE_DIR/test/DebugInfo/dropped-var.sil:9:8: error: no such module 'Swift'
^

Input file: <stdin>
Check file: /home/build-user/swift/test/DebugInfo/dropped-var.sil

-dump-input=help explains the following input dump.

Input was:
<<<<<<
         1: SOURCE_DIR/test/DebugInfo/dropped-var.sil:9:8: error: no such module 'Swift' 
check:4     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
         2: import Swift 
check:4     ~~~~~~~~~~~~~
         3:  ^ 
check:4     ~~~
>>>>>>

[rastogishubham]

@swift-ci please smoke test

[adrian-prantl]

SOURCE_DIR/test/DebugInfo/dropped-var.sil:9:8: error: no such module 'Swift'

Are there no other SIL tests that do something similar to this test that depend on Swift? How do they invoke the compiler?

[rastogishubham]

@adrian-prantl you are right, I am confused, we can see in test/AutoDiff/sil_combine.sil

// RUN: %target-sil-opt -sil-print-types -enable-sil-verify-all %s -sil-combine | %FileCheck %s

// SILCombine tests for differentiation-related instructions.

sil_stage canonical

import Swift
import _Differentiation

And it does pass on the same bot

[rastogishubham]

The problem seems to be the --target=aarch64-apple-darwin on the sil-opt invocation, which makes sense because it is a non-darwin bot that is failing

[rastogishubham]

@swift-ci please smoke test