Handle EINTR on read

It seems read(2) for files may be interrupted on Mac when
ckati is running under a debugger.
diff --git a/fileutil.cc b/fileutil.cc
index a2a0d09..c116f31 100644
--- a/fileutil.cc
+++ b/fileutil.cc
@@ -84,7 +84,7 @@
 
       while (true) {
         char buf[4096];
-        ssize_t r = read(pipefd[0], buf, 4096);
+        ssize_t r = HANDLE_EINTR(read(pipefd[0], buf, 4096));
         if (r < 0)
           PERROR("read failed");
         if (r == 0)