[clang] [clang][CoverageMapping] do not emit gap when either end is an `ImplicitValueInitExpr` (PR #89564)

[Wentao Zhang via cfe-commits]

whentojump wrote:

Fwiw, I uncovered #86998 in the first place when I was compiling this file in Linux kernel: https://elixir.bootlin.com/linux/v6.8.1/source/fs/coredump.c#L545. I can confirm on my local side, with this patch, `fs/coredump.o` can be compiled and instrumented successfully.

I am going to squash merge this PR.

https://github.com/llvm/llvm-project/pull/89564