Add missing random.c patch for Ruby 2.3.2

[joesiewert]

Getting the following message when trying to build Ruby 2.3.2:

ruby-2.3.2 - #extracting ruby-2.3.2 to /home/rof/.rvm/src/ruby-2.3.2....
ruby-2.3.2 - #applying patch /home/rof/.rvm/patches/ruby/ruby_2_3_gcc7.patch.
Patch 'random_c_using_NR_prefix' not found.
There has been an error applying the specified patches. Halting the installation.

It looks like random_c_using_NR_prefix.patch was added in #4048, but did not get included for 2.3.2.

[pkuczynski]

@mpapis doesn't it have to be also added to https://github.com/rvm/rvm/blob/master/patchsets/ruby/2.3.2/default ?

[mpapis]

it is in default already, it was added in #4146

[pkuczynski]

Ah, my bad, sorry!