OSSEC HIDS cc: error trying to exec 'as': execvp:

I am trying to install ossec agent (2.8.1) on sles 11 sp1 and when running the ./install.sh I get this error:

cc: error trying to exec ‘as’: execvp: No such file or directory

I did install make and gcc-c++ , but I have the feeling I am missing packages
in /var/log/messages I dont see any logs regarding ossec

here is the complete error:

5- Installing the system
 - Running the Makefile
cc: error trying to exec 'as': execvp: No such file or directory
./Makeall: line 128: ./isbigendian: No such file or directory
INFO: Little endian set.

 *** Making zlib (by Jean-loup Gailly and Mark Adler)  ***
make[1]: Entering directory `/tmp/ossec-hids-2.8.1/src/external'
cd zlib-1.2.8/; ./configure; make libz.a;
Checking for gcc...
Compiler error reporting is too harsh for ./configure (perhaps remove -Werror).
** ./configure aborting.
make[2]: Entering directory `/tmp/ossec-hids-2.8.1/src/external/zlib-1.2.8'
make[2]: *** No rule to make target `libz.a'.  Stop.
make[2]: Leaving directory `/tmp/ossec-hids-2.8.1/src/external/zlib-1.2.8'
make[1]: *** [libz.a] Error 2
make[1]: Leaving directory `/tmp/ossec-hids-2.8.1/src/external'

Error Making zlib
make: *** [all] Error 1

 Error 0x5.
 Building error. Unable to finish the installation.

The issue is missing a package, but which one

(there are rpm packages for OSSEC and installed them, but they don’t seem to work (to make a long story short))

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