Revert "ModuleInterface: lock .swiftinterface while generating module cache"

[shahmishal]

Reverts #29101

Reverting because this is block full pull request testing:
https://ci.swift.org/job/oss-swift-pr-test/9829/console

19:38:19 Failing Tests (1):
19:38:19     Swift(iphonesimulator-i386) :: Driver/lock_interface.swift

19:36:43 FAIL: Swift(iphonesimulator-i386) :: Driver/lock_interface.swift (11768 of 12515)
19:36:43 ******************** TEST 'Swift(iphonesimulator-i386) :: Driver/lock_interface.swift' FAILED ********************
19:36:43 Script:
19:36:43 --
19:36:43 : 'RUN: at line 1';   rm -rf "/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp" && mkdir -p "/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp"
19:36:43 : 'RUN: at line 2';   echo 'public func foo() {}' > /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/Foo.swift
19:36:43 : 'RUN: at line 3';   /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/bin/swiftc -frontend -target i386-apple-ios7.0  -module-cache-path '/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/swift-test-results/i386-apple-ios7.0/clang-module-cache' -sdk '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.2.sdk' -swift-version 4  -ignore-module-source-info -typo-correction-limit 10 -typecheck -emit-module-interface-path /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/Foo.swiftinterface /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/Foo.swift -enable-library-evolution
19:36:43 : 'RUN: at line 4';   touch /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/main.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-01.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-02.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-03.swift
19:36:43 : 'RUN: at line 5';   echo 'import Foo' > /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-01.swift
19:36:43 : 'RUN: at line 6';   echo 'import Foo' > /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-02.swift
19:36:43 : 'RUN: at line 7';   echo 'import Foo' > /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-03.swift
19:36:43 : 'RUN: at line 8';   env SDKROOT= '/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/bin/swiftc' -toolchain-stdlib-rpath -module-cache-path '/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/swift-test-results/i386-apple-ios7.0/clang-module-cache' -swift-version 4  -Xfrontend -ignore-module-source-info -j20 /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/main.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-01.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-02.swift /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/file-03.swift -I /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp -Xfrontend -Rmodule-interface-rebuild &> /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/result.txt
19:36:43 : 'RUN: at line 9';   '/usr/bin/python' '/Users/buildnode/jenkins/workspace/oss-swift-pr-test/swift/utils/PathSanitizingFileCheck' --sanitize BUILD_DIR='/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64' --sanitize SOURCE_DIR='/Users/buildnode/jenkins/workspace/oss-swift-pr-test/swift' --use-filecheck '/Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/llvm-macosx-x86_64/bin/FileCheck'  /Users/buildnode/jenkins/workspace/oss-swift-pr-test/swift/test/Driver/lock_interface.swift  -check-prefix=CHECK-REBUILD < /Users/buildnode/jenkins/workspace/oss-swift-pr-test/buildbot_incremental/swift-macosx-x86_64/test-iphonesimulator-i386/Driver/Output/lock_interface.swift.tmp/result.txt
19:36:43 --
19:36:43 Exit Code: 1
19:36:43 
19:36:43 Command Output (stderr):
19:36:43 --
19:36:43 <unknown>:0: warning: module interfaces are only supported with Swift language version 5 or later (currently using -swift-version 4)
19:36:43 
19:36:43 --
19:36:43 
19:36:43 ********************