Revert "[Support] Add RetryAfterSignal helper function" and subsequent fix

The fix in r306003 uncovered a pretty fundamental problem that libc++
implementation of std::result_of does not handle the prototype of
open(2) correctly (presumably because it contains ...). This makes the
whole function unusable in its current form, so I am also reverting the
original commit (r305892), which introduced the function, at least until
I figure out a way to solve the libc++ issue.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306005 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/MemoryBuffer.cpp

@@ -240,9 +240,11 @@ getMemoryBufferForStream(int FD, const Twine &BufferName) {
   // Read into Buffer until we hit EOF.
   do {
     Buffer.reserve(Buffer.size() + ChunkSize);
-    ReadBytes = sys::RetryAfterSignal(-1, read, FD, Buffer.end(), ChunkSize);
-    if (ReadBytes == -1)
+    ReadBytes = read(FD, Buffer.end(), ChunkSize);
+    if (ReadBytes == -1) {
+      if (errno == EINTR) continue;
       return std::error_code(errno, std::generic_category());
+    }
     Buffer.set_size(Buffer.size() + ReadBytes);
   } while (ReadBytes != 0);
 
@@ -389,12 +391,13 @@ getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
 
   while (BytesLeft) {
 #ifdef HAVE_PREAD
-    ssize_t NumRead = sys::RetryAfterSignal(-1, ::pread, FD, BufPtr, BytesLeft,
-                                            MapSize - BytesLeft + Offset);
+    ssize_t NumRead = ::pread(FD, BufPtr, BytesLeft, MapSize-BytesLeft+Offset);
 #else
-    ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, BufPtr, BytesLeft);
+    ssize_t NumRead = ::read(FD, BufPtr, BytesLeft);
 #endif
     if (NumRead == -1) {
+      if (errno == EINTR)
+        continue;
       // Error while reading.
       return std::error_code(errno, std::generic_category());
     }