Linux without the GNU toolchain 5105

In theory, you don't need GNU at all; but clearly that is not practical.

In practice, you aren't going to get away from GCC at all. The Linux kernel is developed using GCC, and they do take advantage of GCC specific features. Which is to say the Linux kernel is *not* written in ISO-ANSI Standard C, it is written in GNU C, a different beast.

As a result, you might well get it to compile with something else, such as tcc which has been mentioned, but the results will not be pleasing. You'll never know if it introduces bugs, and at a minimum you'll suffer from tradeoffs, such as the speed of tcc compared to the increased size of the resulting binary. (Using tcc is great for development, but gcc is better for production of a final product.)

As for virtually everything else, there are many embedded systems which basically do not use GNU utils other than the development system (compiler, buttembler, linker etc).

Look up busybox and uClibc projects, which supply the tools and the C library, respectively.

A typical example are the Linksys WRT54G router-wireless units.

As has been suggested by others, take a look at busybox. Note also that most of it can be deleted from a build. Depends on what you want... For example, the Linksys embedded systems don't use the init program from busybox, and instead have a custom init.

Except that *obviously* is not true! (Just look at the prethora of such replacement kernels...)

You are whining. The answers to *all* of your questions are easily found by using google to do a little research. Why ask questions and then argue about the answers that people are kind enough to give you for free?

What kind of scientist goes about it in the way you have?

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