gdb/testsuite: add template for test cases

gdb/testsuite: add template for test cases

The wiki contains a template for new test cases:

    https://sourceware.org/gdb/wiki/GDBTestcaseCookbook#Building_the_Example_Program

... which is helpful, because even after many years I can't write all
the boilerplate for writing a test case without doing some mistakes.

However, I think it would be nice to have it in the tree.  It's much
faster to cp the files than going to the wiki and copy/pasting the
contents.

As a bonus, the copyright years will get updated in these files, unlike
those in the wiki.  So they will always be good when we start a new
test.

If this patch is merged, I plan to change the wiki to just point to
these files.

gdb/testsuite/ChangeLog:

	* gdb.base/template.exp: New.
	* gdb.base/template.c: New.

Change-Id: I7dbf068a043b48f83cc325087d70e868eee998c6