[UpdateTestChecks] Teach the x86 asm parser to skip over the function

begin label emitted for some routines with personality functions and
such.

Without this, we don't even recognize such functions as appearing in the
output and so don't attach any assertions to them. Happy to tweak this
or improve it if folks w/ deeper knowledge of the asm sequences that
show up here want.

llvm-svn: 336987