[meson] Fix handling of HarfBuzz library.
* meson.build (harfbuzz_dep): Do not fall back to HarfBuzz by
default.
Otherwise it causes a dependency cycle:
cairo => fontconfig => freetype2 => harfbuzz => cairo
Meson will still fall back to HarfBuzz subprojects if the `harfbuzz`
option is set to `enabled` instead of `auto` and a
`subprojects/harfbuzz.wrap` file is present. In that case it is the
responsibility of the main project to set the proper options on each
subproject to break the dependency cycle.
Fixes: #1028.
2 files changed
