regex functions: report informative error if not available.

regex functions: report informative error if not available.

When trying to use the new regex functions (match/test/sub/capture/etc)
in a JQ that was compiled without the ONIGURAMA regex library,
report an informative error message instead of a 'not defined' error.

Before:

    $ echo '"foo"' | ./jq-old 'test("foo")'
    jq: error: test/1 is not defined at <top-level>, line 1:
    test("foo")
    jq: 1 compile error

After:

    $ echo '"foo"' | ./jq 'test("foo")'
    jq: error: jq was compiled without ONIGURAMA regex libary. match/test/sub and related functions are not available.