[Clas_offline] a way to build with old PRODUCTION build

[Zhiwen Zhao]

Hi, folks.

As our system has changed to x64, to best way to use clas packages is 
certainly to use the prebuilt /group/clas/builds/32Bit or 64Bit
If you want your own build, check out the svn tree and build it.

But for some old personal code, particularly if you want your old code 
work so that you can compare the result with newly built code. You still 
want the possibility to build with the previous prebuilt.
For example, my code was built with
/group/clas/builds/PRODUCTION (a link to release-f8-2)
So now if I want to compile it again, I have to request access ifarml5 
from Sandy.
Or alternatively, I can do following.

login into ifarml6
cp /group/clas/builds/PRODUCTION/packages/cms/jlab.cshrc ./
modify a couple lines in jlab.cshrc to
setenv OSCLAS       LinuxRHFC8
setenv OS_NAME      LinuxRHFC8
setenv ROOTSYS /apps/root/5.26-00/root
then source jlab.cshrc
This will make the system think you are still using the old LinuxRHFC8 
which the release-f8-2 was built upon.

Then you have to modify your Makefile to let it compile things in 32bits.
Generally, it's done by give g++ and gfortran the -m32 option
If your make file is based on clas Makefile which means you have line 
like "include $(CLAS_CMS)/Makefile", you want to add a couple lines
CFLAGS += -m32
CPPFLAGS += -m32
CXXFLAGS += -m32
FFLAGS += -m32
FLDFLAGS += -m32
OS_NAME=LinuxRHFC8

Finally, you have newly compiled code by a newer gcc with the old 
PRODUCTION build.

Zhiwen