[clang] [clang][analyzer] Improve modeling of 'execv' and 'execvp' in StdLibraryFunctionsChecker (PR #78930)

[Ben Shi via cfe-commits]

benshi001 wrote:

> Test for these functions can be added to file std-c-library-functions-POSIX.c (with check of return value and `errno`).

I will put them into `errno-stdlibraryfunctions.c`, which seems better.

https://github.com/llvm/llvm-project/pull/78930