[BPF] Remove exit-on-error flag in test (PR27766)

The exit-on-error flag on the many_args1.ll test is needed to avoid an
unreachable in BPFTargetLowering::LowerCall. We can also avoid it by ignoring
any superfluous arguments to the call (i.e. any arguments after the first 5).

Fixes PR27766

llvm-svn: 270419