RFR 8233880: Support compilers with multi-digit major version numbers

[Florian Weimer]

* Tim Bell:

> Florian:
>
>> The current regular expression only matches one digit before the first
>> dot.
>>
>> Bug: <https://bugs.openjdk.java.net/browse/JDK-8233880>
>> Webrev: <http://cr.openjdk.java.net/~fweimer/8233880/webrev.01/>
>>
>> Tested against GCC 10.0.0.  configure no longer prints a C/C++ version
>> mismatch warning.
>
> Looks good.

Would you please sponsor this change for me?  Thanks.

Florian