rand: include the CPU source in a build.

Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/12267)

.travis.yml

@@ -41,7 +41,7 @@ jobs:
           env: CONFIG_OPTS="" DESTDIR="_install"
         - os: linux
           compiler: clang
-          env: CONFIG_OPTS="no-asm no-makedepend enable-buildtest-c++ --strict-warnings -D_DEFAULT_SOURCE" BUILDONLY="yes" CHECKDOCS="yes" CPPFLAGS="-ansi"
+          env: CONFIG_OPTS="no-asm no-makedepend enable-buildtest-c++ --strict-warnings --with-rand-seed=rdcpu,os -D_DEFAULT_SOURCE" BUILDONLY="yes" CHECKDOCS="yes" CPPFLAGS="-ansi"
         - os: osx
           compiler: gcc
         - os: osx