[clang] [clang][analyzer] fix false positive of BlockInCriticalSectionChecker (PR #127049)

[via cfe-commits]

flovent wrote:

i did something not right about git, so i closed before PR #126752 
@Xazax-hun @whisperity please take another look
i changed the variable name releated to marco `O_NONBLOCK`;
make the first letter uppercase for local variable.
add new lines to testcase file.
and update the way i checks for NON_BLOCK descriptor, using set to store `open`'s return value

https://github.com/llvm/llvm-project/pull/127049