Fix 6502 cbmbasic_lib build breakage on Linux
Fix 6502 cbmbasic_lib build breakage on Linux

Fixes the following build error:

  cc1plus: warnings being treated as errors
  /home/penberg/src/libcpu/test/6502/cbmbasic_lib.cpp: In function ‘void LOAD()’:
  /home/penberg/src/libcpu/test/6502/cbmbasic_lib.cpp:392: error: ignoring return value of ‘char* getcwd(char*, size_t)’, declared with attribute warn_unused_result
  make[3]: *** [test/6502/CMakeFiles/test_6502.dir/cbmbasic_lib.cpp.o] Error 1

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cs.helsinki.fi>

ukatemi/libcpu,curtiszimmerman/libcpu,ukatemi/libcpu,monocasa/libcpu,libcpu/libcpu,libcpu/libcpu,ukatemi/libcpu,monocasa/libcpu,curtiszimmerman/libcpu,curtiszimmerman/libcpu,glguida/libcpu,libcpu/libcpu,ukatemi/libcpu,curtiszimmerman/libcpu,monocasa/libcpu,monocasa/libcpu,glguida/libcpu,glguida/libcpu,libcpu/libcpu,glguida/libcpu