Return shared library build support.

[cfnptr]

We are using static zlib library on linux, which is built without -fPIC flag. And because of that we can't use it to build shared library.

Error:

/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libz.a(zutil.o): warning: relocation against `z_errmsg' in read-only section `.text'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libz.a(zutil.o): relocation R_X86_64_PC32 against symbol `z_errmsg' can not be used when making a shared object; recompile with -fPIC

Current solution is to disable shared lib build. 48a6708