Remove awk dependency when building using CMake. Before this awk was required

Remove awk dependency when building using CMake. Before this awk was required
for -DWITH_MODULES option.

* build/build-modules-c.cmake:
  (generate_builtin_modules_c): Function to generate modules.c.

* CMakeLists.txt
  (): Use generate_builtin_modules_c() instead of `awk -f build/build-modules-c.awk`
  to generate modules.c file.

* README.cmake:
  (Prerequisites, How to build): Do not mention awk as prerequisite.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1919413 13f79535-47bb-0310-9956-ffa450edef68