Ensure we're writing to stderr in the builder

http://hydra.nixos.org/build/17862041

src/libstore/build.cc

@@ -2166,7 +2166,7 @@ void DerivationGoal::runChild()
         restoreSIGPIPE();
 
         /* Indicate that we managed to set up the build environment. */
-        writeToStderr("\n");
+        writeFull(STDERR_FILENO, "\n");
 
         /* Execute the program.  This should not return. */
         execve(program.c_str(), (char * *) &args[0], (char * *) envArr);
@@ -2174,7 +2174,7 @@ void DerivationGoal::runChild()
         throw SysError(format("executing ‘%1%’") % drv.builder);
 
     } catch (std::exception & e) {
-        writeToStderr("while setting up the build environment: " + string(e.what()) + "\n");
+        writeFull(STDERR_FILENO, "while setting up the build environment: " + string(e.what()) + "\n");
         _exit(1);
     }
 }
@@ -2487,7 +2487,7 @@ void DerivationGoal::handleChildOutput(int fd, const string & data)
             BZ2_bzWrite(&err, bzLogFile, (unsigned char *) data.data(), data.size());
             if (err != BZ_OK) throw Error(format("cannot write to compressed log file (BZip2 error = %1%)") % err);
         } else if (fdLogFile != -1)
-            writeFull(fdLogFile, (unsigned char *) data.data(), data.size());
+            writeFull(fdLogFile, data);
     }
 
     if (hook && fd == hook->fromHook.readSide)

src/libstore/gc.cc

@@ -191,7 +191,7 @@ void LocalStore::addTempRoot(const Path & path)
     lockFile(fdTempRoots, ltWrite, true);
 
     string s = path + '\0';
-    writeFull(fdTempRoots, (const unsigned char *) s.data(), s.size());
+    writeFull(fdTempRoots, s);
 
     /* Downgrade to a read lock. */
     debug(format("downgrading to read lock on ‘%1%’") % fnTempRoots);
@@ -231,7 +231,7 @@ static void readTempRoots(PathSet & tempRoots, FDs & fds)
         if (lockFile(*fd, ltWrite, false)) {
             printMsg(lvlError, format("removing stale temporary roots file ‘%1%’") % path);
             unlink(path.c_str());
-            writeFull(*fd, (const unsigned char *) "d", 1);
+            writeFull(*fd, "d");
             continue;
         }
 

src/libstore/pathlocks.cc

@@ -33,7 +33,7 @@ void deleteLockFile(const Path & path, int fd)
        other processes waiting on this lock that the lock is stale
        (deleted). */
     unlink(path.c_str());
-    writeFull(fd, (const unsigned char *) "d", 1);
+    writeFull(fd, "d");
     /* Note that the result of unlink() is ignored; removing the lock
        file is an optimisation, not a necessity. */
 }