Enable -fPIC to fix linking static libraries when building with Qt6

Otherwise the build would fail:
/usr/lib64/gcc/x86_64-suse-linux/11/../../../../x86_64-suse-linux/bin/ld: ../lib/libkonsoleprivate_core.a(ShellCommand.cpp.o): warning: relocation against `_ZN7QString6_emptyE@@Qt_6' in read-only section `.text'
/usr/lib64/gcc/x86_64-suse-linux/11/../../../../x86_64-suse-linux/bin/ld: ../lib/libkonsoleprivate_core.a(ShellCommand.cpp.o): relocation R_X86_64_PC32 against symbol `_ZN10QByteArray6_emptyE@@Qt_6' can not be used when making a shared object; recompile with -fPIC
/usr/lib64/gcc/x86_64-suse-linux/11/../../../../x86_64-suse-linux/bin/ld: final link failed: bad value

This seems to affect both STATIC and OBJECT CMake library types.