sudo -k before calling build scripts

Potentially build scripts would call sudo, if so we don't want that to automatically succeed just because the time-period in which sudo works is still active after a previous incantation.

Closes Homebrew#10629.

In fact I don't see how this can have been the problem, but if this isn't the problem then I don't see what else can be the problem.

Library/Homebrew/build.rb

@@ -27,6 +27,11 @@
     # dev tools into /usr/bin as a default
     ENV.prepend 'PATH', MacOS.dev_tools_path, ':' unless ORIGINAL_PATHS.include? MacOS.dev_tools_path
 
+    # Force any future invocations of sudo to require the user's password to be
+    # re-entered. This is in-case any build script call sudo. Certainly this is
+    # can be inconvenient for the user. But we need to be safe.
+    system "/usr/bin/sudo -k"
+
     install(Formula.factory($0))
   rescue Exception => e
     if ENV['HOMEBREW_ERROR_PIPE']