#99: Only use CMAKE_POSITION_INDEPENDENT_CODE when building bindings

[cwschilly]

Fixes #99

[pierrepebay]

Looks good. Out of curiosity, what is the error when building the bindings without this option turned on?

[cwschilly]

Looks good. Out of curiosity, what is the error when building the bindings without this option turned on?

@pierrepebay

[ 98%] Linking CXX shared module vttv.cpython-39-x86_64-linux-gnu.so
/usr/bin/ld: ../../lib/fmt/libfmt-vtd.a(format.cc.o): warning: relocation against `_ZTVN3fmt2vt12system_errorE' in read-only section `.text._ZN3fmt2vt12system_errorC2IJEEEiNS0_17basic_string_viewIcEEDpRKT_[_ZN3fmt2vt12system_errorC5IJEEEiNS0_17basic_string_viewIcEEDpRKT_]'
/usr/bin/ld: ../../src/libvt-tv.a(render.cc.o): relocation R_X86_64_PC32 against symbol `_ZN2vt2tv14compareObjectsERKSt4pairINS0_10ObjectWorkEmES5_' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
make[2]: *** [bindings/python/CMakeFiles/vttv.dir/build.make:142: bindings/python/vttv.cpython-39-x86_64-linux-gnu.so] Error 1
make[1]: *** [CMakeFiles/Makefile2:1784: bindings/python/CMakeFiles/vttv.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

[nlslatt]

I'm not sure if there's another way to fix the link error, but this works at least for now.