jit.exp: Don't drop the extension from the testcase when naming executable

jit.exp: Don't drop the extension from the testcase when naming executable

gcc/jit/ChangeLog:
	* docs/internals/index.rst: Update to reflect that built
	testcases are now test-foo.c.exe, rather than test-foo.exe.
	* docs/_build/texinfo/libgccjit.texi: Regenerate.

gcc/testsuite/ChangeLog:
	* jit.dg/jit.exp (jit-dg-test): Remove "rootname" call when
	generating name of built executable.

From-SVN: r219312