Revert r280137 and 280139 and subsequent build fixes

Revert r280137 and 280139 and subsequent build fixes

The rewrite of StringExtractor::GetHexMaxU32 changes functionality in a way which makes
lldb-server crash. The crash (assert) happens when parsing the "qRegisterInfo0" packet, because
the function tries to drop_front more bytes than the packet contains. It's not clear to me
whether we should consider this a bug in the caller or the callee, but it any case, it worked
before, so I am reverting this until we can figure out what the proper interface should be.

llvm-svn: 280207