Fix CUDA linking error by ensuring -fPIC for position-independent code

[mz2]

Resolves a linker error when building with feature cuda, such that nvcc compiled & linked objects get compiled with position-independent code (-fPIC). I noticed that this was not getting done when building whisper-rs into https://github.com/mz2/pipescribe: when enabling the cuda feature, cargo, the following linker error would occur:

...
"-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/home/mz2/Developer/pipescribe/gui/rust/target/debug/deps/librust_lib_pipescribe.so" "-Wl,--gc-sections" "-shared" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use --verbose to show all linker arguments
  = note: /usr/bin/ld: /home/mz2/Developer/pipescribe/gui/rust/target/debug/deps/libwhisper_rs_sys-193aab817605690a.rlib(fattn.cu.o): warning: relocation against stderr@@GLIBC_2.2.5' in read-only section .text'
          /usr/bin/ld: /home/mz2/Developer/pipescribe/gui/rust/target/debug/deps/libwhisper_rs_sys-193aab817605690a.rlib(mmq-instance-iq1_s.cu.o): relocation R_X86_64_PC32 against symbol stderr@@GLIBC_2.2.5' 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

I have confirmed this to be fixed with the changes in this PR.

[tazz4843]

Sorry this took me so long to get around to, looks good. Thanks :)