Bug#997049: mapnik silently drops PROJ support with PROJ 8.1.1

[Adrian Bunk]

Source: mapnik
Version: 3.1.0+ds-1
Severity: important
Forwarded: https://github.com/mapnik/mapnik/pull/4202

https://buildd.debian.org/status/fetch.php?pkg=mapnik&arch=amd64&ver=3.1.0%2Bds-1%2Bb2&stamp=1634940413&raw=0

...
Checking for C library proj... no
Could not find optional header or shared library for proj
Checking for C library png... yes
Checking for C library webp... yes
Checking for C library tiff... yes
Checking for PROJ_LIB directory...Failed to detect (mapnik-config will have null value)
...
Note: will build without these OPTIONAL dependencies:
   - proj (Proj.4 C Projections library | configure with PROJ_LIBS & PROJ_INCLUDES | more info: http://trac.osgeo.org/proj/)
...