grass76 and 78 won't compile r.solpos and r.heliosat

[gjscheer-ucd]

GRASS 7.8.0 (cimis):~/gdb > g.extension extension=r.solpos url=/home/cimis/src/r.solpos
Fetching <r.solpos> from </home/cimis/src/r.solpos> (be patient)...
Compiling...
In file included from main.c:26:0:
/usr/lib/grass78/include/grass/gprojects.h:23:10: fatal error: proj.h: No such file or directory
#include <proj.h>
^~~~~~~~
compilation terminated.
make: *** [OBJ.x86_64-pc-linux-gnu/main.o] Error 1
ERROR: Compilation failed, sorry. Please check above error messages.

The following PROJ pkgs are installed:

ii libgeo-proj4-perl:amd64 1.09-1 amd64 PROJ.4 library for cartographic projections
ii libproj-dev:amd64 4.9.3-2 amd64 Cartographic projection library (development files)
ii libproj12:amd64 4.9.3-2 amd64 Cartographic projection library
ii libproj13:amd64 5.2.0-1~bionic0 amd64 Cartographic projection library
ii proj-bin 4.9.3-2 amd64 Cartographic projection library (tools)
ii proj-data 4.9.3-2 all Cartographic projection filter and library (datum package)
ii python-pyproj 1.9.5.1-3build1 amd64 Python interface to PROJ.4 library