Read from the error pipe in a separate thread

If the build process tries to write more bytes than will fit in the pipe
buffer, it will block until the parent process does a read. However, the
parent process will only do a read after the child process has exited or
died, leading to a deadlock. Fix this by doing the read in a separate
thread.

Library/Homebrew/formula_installer.rb

@@ -515,8 +515,9 @@ class FormulaInstaller
 
     ignore_interrupts(:quietly) do # the child will receive the interrupt and marshal it back
       write.close
+      thr = Thread.new { read.read }
       Process.wait(pid)
-      data = read.read
+      data = thr.value
       read.close
       raise Marshal.load(data) unless data.nil? or data.empty?
       raise Interrupt if $?.exitstatus == 130