modified:   CMakeLists.txt

Add a version variable so it gets added to the pkg-config file.

Using optimized byte swaps reduced portability for no real benefit,
since they are in parts of the code that represent a tiny fraction
of the execution time.  So a simple definition of a byte swap is
now used.

SunOS 4.1 claims that it is __STDC__, but it does not have strerror
in string.h.  Instead of using __STDC__, this puts a direct test
for strerror in configure, and uses that information in gzguts.h.

SunOS 4.1 doesn't have memmove(), and there may be others.  memcpy()
should not be used for overlapping copies, so here a simple copy is
implemented that works for the particular direction of the overlap,
which is where the destination precedes the source.