[meson] Fix build with -Dfuzzer_ldflags on meson >= 1.4.0 The failing-alloc.c file is appended to various hb_sources_* as a string, but on >= 1.4.0 we call full_path() on the sources, and this works only with file objects. Fixes https://github.com/harfbuzz/harfbuzz/pull/5340