than ".so".  The old extension conflicted with well-established
naming conventions for dynamically loadable modules.

The "clean" targets continue to remove ".so" files too, to deal with
old systems.

non-problems for elf -- `ld -elf -O foo.tmp -x -r foo' apparently puts
the result in a.out so it has essentially no effect.

shared versions should not need to add -lm unless the program uses libm
itself.  Strictly speaking, libg++ depends on libstdc++, but libstdc++
has dynamic dependencies on some exception tables and binutils doesn't
seem to like it when a secondary library has undefined references.  It
doesn't seem to care when -lstdc++ is added on the command line to ld
though.  Anyway, the c++ driver adds -lstdc++ explicitly, so that should
be OK.  c++ also adds -lm explicitly too, even though it wouldn't need
to now. [except for statically linked binaries as .a files don't have an
equivalent of automatic internal shared object dependencies.]

fix of putting generated source files in SRCS breaks many special
cases (many dependencies had to be incomplete for ${.ALLSRC}
not to give .h files that would break compiling with c++ -c).
Reduce these special cases to the general case so that SRCS works
normally and bsd.lib.mk handles most of the complications.  Now
we only have to duplicate rules from bsd.lib.mk to add special
CFLAGS in some cases.

('_vt.' vs '__vt$')

Reviewed by:	bde