databases/pspg: fix build on GCC architectures

Use new GCC:
src/pspg.c: In function 'main':
src/pspg.c:2743: error: 'SIZEOF_WCHAR_T' undeclared (first use in this function)
src/pspg.c:2743: error: (Each undeclared identifier is reported only once
src/pspg.c:2743: error: for each function it appears in.)

Approved by: mentors (implicit approval)