Disable 32-bit assembly on Apple platforms. (#109)

Motivation:

The 32-bit assembly in BoringSSL doesn't assemble correctly on 32-bit
apple platforms. It took us a while to notice because we previously
haven't had any supported 32-bit platforms. NIOSSL still doesn't really
support any 32-bit Apple platforms, as all production use on those
platforms should use NIOTS, but there's no excuse for the compilation
failures really.

Modifications:

Remove assembly acceleration on 32-bit Apple platforms.

Result:

Better compilation on 32-bit Apple platforms.

Package.swift

@@ -22,7 +22,7 @@ import PackageDescription
 // Sources/CNIOBoringSSL directory. The source repository is at
 // https://boringssl.googlesource.com/boringssl.
 //
-// BoringSSL Commit: ff62b38b4b5a0e7926034b5f93d0c276e55b571d
+// BoringSSL Commit: cef9d3f38d72f13412c79157c25753e22cb05f7e
 
 let package = Package(
     name: "swift-nio-ssl",