tools: update tooling to work with new macOS CLI …

Using High Sierra and `xcode-select --install` without installing full
Xcode, our build tooling breaks due to faulty regular expressions.

Update the `configure` script in our project root directory to handle
multi-digit version numbers.

`tools/gyp` and `deps/npm/node_modules/node-gyp` still need to be
updated for a complete fix.

PR-URL: #21173
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

configure

@@ -610,7 +610,7 @@ def get_llvm_version(cc):
 
 def get_xcode_version(cc):
   return get_version_helper(
-    cc, r"(^Apple LLVM version) ([5-9]\.[0-9]+)")
+    cc, r"(^Apple LLVM version) ([0-9]+\.[0-9]+)")
 
 def get_gas_version(cc):
   try: