Harmonize the make variables across all known platforms families

The make variables LIB_CFLAGS, DSO_CFLAGS and so on were used in
addition to CFLAGS and so on.  This works without problem on Unix and
Windows, where options with different purposes (such as -D and -I) can
appear anywhere on the command line and get accumulated as they come.
This is not necessarely so on VMS.  For example, macros must all be
collected and given through one /DEFINE, and the same goes for
inclusion directories (/INCLUDE).

So, to harmonize all platforms, we repurpose make variables starting
with LIB_, DSO_ and BIN_ to be all encompassing variables that
collects the corresponding values from CFLAGS, CPPFLAGS, DEFINES,
INCLUDES and so on together with possible config target values
specific for libraries DSOs and programs, and use them instead of the
general ones everywhere.

This will, for example, allow VMS to use the exact same generators for
generated files that go through cpp as all other platforms, something
that has been i...