stdint.h: Next attempt at making this work with various compilers

stdint.h: Next attempt at making this work with various compilers

Newer GCC with GNU LIBC do not like our minimalistic version of
stdint.h and will have conflicts. Older GCC with older C Libs do
not have a stdint.h yet and the #include_next trick is failing. To
make matters worse NEWLIB does not export its version via the
pre-processor.

We will have to guess once more about the compiler. This code now
assumes that if we have a GCC < 4 that it does not have a stdint.h
and we will not try to include the next stdint.h file.