[UpdateTestChecks] Allow Lbegin_func without a leading period
On mingw/i686, local labels don't start with a leading period.
Also escape the leading period, as it previously could match
any char.
Differential Revision: https://reviews.llvm.org/D61254
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@359497 91177308-0d34-0410-b5e6-96231b3b80d8