[libc] fix -Wmacro-redefined (#75261)

When building with compiler-rt enabled, warnings such as the following
are
observed:


llvm-project/llvm/build/projects/compiler-rt/../libc/include/llvm-libc-macros/linux/sys-stat-macros.h:46:9:
    warning: 'S_IXOTH' macro redefined [-Wmacro-redefined]
    #define S_IXOTH 00001
            ^

llvm-project/llvm/build/projects/compiler-rt/../libc/include/llvm-libc-macros/linux/fcntl-macros.h:61:9:
    note: previous definition is here
    #define S_IXOTH 01
            ^
It looks like we have these multiply defined. Deduplicate these flags;
users
should expect to find them in sys/stat.h. S_FIFO was wrong anyways
(should
have been S_IFIFO).