Portable makefiles - portable shell commands?

[address@hidden]

Hello all!

I was wondering how GNU make can best be used to build programs on
multiple platforms (and on each platform possibly with multiple
compilers), like on Win32 with MSVC and OpenWatcom, on Linux with g++,
etc.

Part of the answer is of course already discussed in
http://make.paulandlesley.org/multi-arch.html , and thus my goal is to
be able to use a single Makefile for all platforms and all compilers
that I support for my project.

All that I'm still really concerned about is the portability of the
shell commands that are used e.g. for the "clean" targets: I cannot
simply get make from
http://prdownloads.sf.net/mingw/mingw32-make-3.80.0-3.exe?download 
*and* write for example    rm -f $(shell find . -name "*~")    as a
shell command for the clean target, can I?

How can this problem best be addressed?  sh.exe for Win32? Conditionals
in the Makefile? ...?
I'd be very grateful for some advice.

Thank you very much in advance.

Best regards,
Carsten

http://www.Ca3D-Engine.de