In early bootstrap, use byte-compiled compiler to native compile first files

In early bootstrap, use byte-compiled compiler to native compile first files

This speeds up a make bootstrap by around 15%.

* lisp/Makefile.in (BYTE_COMPILE_FLAGS): set a value specific to compile-first
which doesn't contain the setting of Emacs variable load-prefer-newer.
Add a new make hunk which byte-compiles (rather then native compiles) when the
environment variable ANCIENT is "yes".  Set the date of the .elc files built
to 1971-01-01 to cause a second compilation of them later.

* src/Makefile.in: Add an extra invocation of directory lisp's MAKE with
target compile-first and the flag environment variable ANCIENT set to yes.

* src/verbose.mk.in: When ANCIENT is yes, output ELC, not ELC+ELN for
AM_V_ELC.