Fix require and supress error messages of byte compile

[zonuexe]

declare-function is a directive that notifies the byte compiler of function definition information.
This suppresses unnecessary error messages during byte compilation.

Before

% make
emacs -Q -batch -L . --eval \
	"(progn \
	   (require 'package) \
	   (package-generate-autoloads \"php-mode\" default-directory))"
Generating autoloads for php-cc-mode.el...
Generating autoloads for php-cc-mode.el...done
Generating autoloads for php-core.el...
Generating autoloads for php-core.el...done
Generating autoloads for php-mode-test.el...
Generating autoloads for php-mode-test.el...done
Generating autoloads for php-mode.el...
Generating autoloads for php-mode.el...done
Generating autoloads for php-project.el...
Generating autoloads for php-project.el...done
Generating autoloads for tiny-init.el...
Generating autoloads for tiny-init.el...done
Wrote /Users/megurine/repo/emacs/php-mode/php-mode-autoloads.el
Wrote /Users/megurine/repo/emacs/php-mode/php-mode-autoloads.el
emacs -Q -batch -L . -f batch-byte-compile php-project.el
emacs -Q -batch -L . -f batch-byte-compile php-mode.el

In end of data:
php-mode.el:1854:1:Warning: the following functions are not known to be
    defined: package-desc-status, package-version-join, package-desc-version,
    custom-group-members, semantic-create-imenu-index
emacs -Q -batch -L . -f batch-byte-compile php-mode-test.el

After

% make
emacs -Q -batch -L . --eval \
	"(progn \
	   (require 'package) \
	   (package-generate-autoloads \"php-mode\" default-directory))"
Generating autoloads for php-cc-mode.el...
Generating autoloads for php-cc-mode.el...done
Generating autoloads for php-core.el...
Generating autoloads for php-core.el...done
Generating autoloads for php-mode-test.el...
Generating autoloads for php-mode-test.el...done
Generating autoloads for php-mode.el...
Generating autoloads for php-mode.el...done
Generating autoloads for php-project.el...
Generating autoloads for php-project.el...done
Generating autoloads for tiny-init.el...
Generating autoloads for tiny-init.el...done
Wrote /Users/megurine/repo/emacs/php-mode/php-mode-autoloads.el
Wrote /Users/megurine/repo/emacs/php-mode/php-mode-autoloads.el
emacs -Q -batch -L . -f batch-byte-compile php-project.el
emacs -Q -batch -L . -f batch-byte-compile php-mode.el
emacs -Q -batch -L . -f batch-byte-compile php-mode-test.el