[cmake][xcode-toolchain] add support for major Xcode version >= 10

The regex that extracts the Xcode version should support major versions with two
digits.

rdar://41465184


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335801 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed