build swift-nio-example failed get error, memory file not found

### Expected behavior
_[what you expected to happen]_
build success
### Actual behavior
_[what actually happened]_
```
Resolving https://github.com/apple/swift-nio at 2.18.0
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/ssl/tls_record.cc:109:
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_ssl.h:145:
/Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_base.h:478:10: fatal error: 'memory' file not found
#include
^~~~~~~~
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/ssl/tls13_enc.cc:15:
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_ssl.h:145:
/Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_base.h:478:10: fatal er

In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/ssl/tls_method.cc:57:
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_ssl.h:145:
/Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_base.h:478:10: fatal error: 'memory' file not found
#include
^~~~~~~~
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/ssl/tls13_server.cc:15:
In file included from /Users/aeris/hswork/http2/swift-nio-examples/http2-client/.build/checkouts/swift-nio-ssl/Sources/CNIOBoringSSL/include/CNIOBoringSSL_ssl.h:145:

^~~~~~~~
1 error generated.
1 error generated.
[6/435] Compiling tls_method.cc
```
### Steps to reproduce

1. git clone https://github.com/apple/swift-nio-examples.git
2. cd swift-nio-examples
3. cd http2-client
4. swift build

### If possible, minimal yet complete reproducer code (or URL to code)

_[anything to help us reproducing the issue]_

### version/commit hashes from all involved dependencies

_[tag/commit hash]_

### Swift & OS version (output of `swift --version && uname -a`)
swift version: swift/5.2.4
macos:10.15.4

Start in the http2-client example by reproducing the reported `swift build` command. Inspect the CNIOBoringSSL build failure at `Sources/CNIOBoringSSL/include/CNIOBoringSSL_base.h:478` using Swift 5.2.4 on macOS 10.15.4 and swift-nio 2.18.0. Done means the example builds successfully without the `'memory' file not found` error.

Written by the indexing model from the issue text.