Fix configure script to work with Apple Clang 10

[saagarjha]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

This is a simple fix to the configure script so it doesn't spuriously drop out for newer versions of Apple's Clang:

$ clang --version
Apple LLVM version 10.0.0 (clang-1000.10.25.5)
Target: x86_64-apple-darwin18.0.0
Thread model: posix
InstalledDir: /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

Please do let me know if there's something wrong with my implementation; I haven't tested this on systems other than macOS so it might have silently broke something there.

[apapirovski]

Hi @saagarjha, thanks for taking this on. It appears there's already an earlier PR implementing a similar change: #21183

[saagarjha]

Sorry, my bad. I should have searched before making the pull request rather than checking when I had the issue yesterday. However, I did look through that pull request, it seems like my code has an additional patch that @mistydemeo's branch doesn't in get_xcode_version. Without it, the configure script halts:

$ ./configure
ERROR: Did not find a new enough assembler, install one or build with
       --openssl-no-asm.
       Please refer to BUILDING.md

[apapirovski]

@saagarjha See #21173 for that.

[saagarjha]

Ah, got it. In that case I guess I'll close this pull request and let you guys merge those instead. Though, might I suggest using Python's built-in tuple comparison operator rather than rolling our own?