Rollback "[Support] Add RetryAfterSignal helper function"

Rollback "[Support] Add RetryAfterSignal helper function"

This rollback is necessary to avoid the following building error:

In file included from external/llvm70/lib/Support/Path.cpp:1082:
external/llvm70/lib/Support/Unix/Path.inc:770:19: error: no matching function for call to 'RetryAfterSignal'
  if ((ResultFD = sys::RetryAfterSignal(-1, open, P.begin(), OpenFlags, Mode)) <
                  ^~~~~~~~~~~~~~~~~~~~~
external/llvm/lib/Support/../../include/llvm/Support/Errno.h:34:13:
note: candidate template ignored: couldn't infer template argument 'Fun'
inline auto RetryAfterSignal(const FailT &Fail, const Fun &F,
            ^
1 error generated.

Fixes: d04333d38b (Recommit "[Support] Add RetryAfterSignal helper function")