cmake: Simplify -E command line processing

Check for "cmake -E ..." up front (along with "cmake --build ...") and
skip normal command line processing.  Drop the special handling for -E
from the normal processing to simplify things.  Strictly speaking, it
was previously possible to invoke command mode with -E anywhere in the
command line e.g. "cmake echo -E message" or "cmake echo message -E",
but no one should be using it as it was not documented and looks
strange.
Merge topic 'simplify-cmake-E-command-line' into next

d4c3de2 cmake: Simplify -E command line processing