meson: Fix ccache issues when using precompiled headers with gcc

meson: Fix ccache issues when using precompiled headers with gcc

Unfortunately the combination of gcc, precompiled headers, ccache and meson
currently is not safe without further options. The dependencies emitted by gcc
are insufficient to trigger rebuilds when headers "below" the precompiled
headers are changed. Whether that's a ccache, gcc or meson bug is
debatable. Luckily gcc's -fpch-deps option fixes the issue.

This problem occasionally leads to build failures, e.g. if only c.h,
postgres.h or pg_config_manual.h change. That's e.g. the case when creating a
new major version branch.

Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/CAN55FZ0tqR6Xz%3DiVFLc1BBoLOEHU775ARhcGYwggHA3XLA%3DoQg%40mail.gmail.com
Discussion: https://postgr.es/m/CA+hUKG+s7Yvt0PUnSQUEjCjysV-7-51n9B1h468Le3VJi0x4ZQ@mail.gmail.com
Discussion: https://postgr.es/m/phsrssp75npoyalqsolcd7fmnmlbzbmquc2p7w7mqjlw7432jk@bzskz3luyjvb
Discussion: https://github.com/ccache/ccache/issues/1686
Backpatch-through: 16, where meson support was added