fix incorrect application of visibility to Scrt1.o

fix incorrect application of visibility to Scrt1.o

commit de2b67f8d41e08caa56bf6540277f6561edb647f attempted to avoid
having vis.h affect crt files, but the Makefile variable used,
CRT_LIBS, refers to the final output copies in the lib directory, not
the copies in the crt build directory, and thus the -DCRT was not
applied.

while unlikely to be noticed, this regression probably broke
production of PIE executables whose main functions are not in the
executable but rather a shared library.