Share cFlags, tidyFlags, etc. in a module

* In builder.go, share common flags in a module.
  * This replaces the sharing of cflags/cppflags/asflags in cc.go.
  * A unit test in apex_test.go now fails and is commented out.
    It is a failing test hidden by old optimization in cc.go.
* In module.go, expand the reference variable $someflags<n>,
  or ${someflags<n>} to keep many existing unit tests work as is.
* The build.ninja size was reduced from 8.1GB to 6.2GB,
  for aosp_arm64-eng WITH_TIDY=1 USE_RBE=true,
  and from 7.5GB to 5.6GB when USE_RBE is 0.
  Content of build.ninja is also more readable and searchable.
  Read/write build.ninja times are also reduced,
  depending on disk I/O speed.

Test: make WITH_TIDY=1
Change-Id: I17f96adf4844136d52e5d40f57a19d9e290162b7