error: postgresql extension pg_math in jail

Hello

I would install pg_math.

Inside a jail I install postgresql. 
--> It works fine. 

export UNAME_r=13.1-RELEASE-p3
ALLOW_UNSUPPORTED_SYSTEM=1 portupgrade -N gsl
--> no error

cd pg_curl 
gmake install clean 
--> here I get the following error:

ld: error: unable to find library -lgsl
ld: error: unable to find library -lgslcblas
cc: error: linker command failed with exit code 1 (use -v to see invocation)
gmake: ***
[/usr/local/lib/postgresql/pgxs/src/makefiles/../../src/Makefile.port:14:
pg_math.so] Error 1

What should I do?
(Do you need more information?)

Franz