Rearrange build process cleanup to avoid spawning a reader thread

This is a follow-up to bbf9f7460fc8e6e4c63f5bbe8630b11ca53f3710.

If we read from the pipe before calling Process.wait, we can avoid
spawning a thread to do the read while continuing to avoid the deadlock
that the thread was introduced to solve.

Library/Homebrew/formula_installer.rb

@@ -505,10 +505,9 @@ 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 = thr.value
+      data = read.read
       read.close
+      Process.wait(pid)
       raise Marshal.load(data) unless data.nil? or data.empty?
       raise Interrupt if $?.exitstatus == 130
       raise "Suspicious installation failure" unless $?.success?