Cheatsheet for building gcc

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

with the changes to the build system in the last few months, I am having
problems to do some things I am used to do during development.  I found
more or less satisfactory procedures for most them, however, I would
like to know the "official" way how to achieve those effects (and to put
the created "cheatsheet" to wiki, so that people do not have to reinvent
the wheel).  All the solutions should be for gcc configured without any
special options (except for --enable-languages and --target):

Example:

Q1) How to bootstrap the compiler, including all libraries?
A1) "make" from the top directory

Could some of the build system experts please provide the answers
for the following questions?

Q2) How to bootstrap the compiler, but not build any time consuming
    libraries (libjava, libstdc++)?

Q3) How to compile just the stage1 compiler + the basic runtime
    (libgcc, libmudflap, libgomp)?

Q4) How to compile all the libraries (libjava, ...) using the stage1
    compiler?

Q5) How to clean up everything (including the stage1 compiler, but
    excluding makefiles, so that I can build everything from scratch,
    but configure does not have to be run)?

Q6) How to clean up everything except for the stage1 compiler and
    its runtime (libgcc, libmudflap, libgomp)?

And of course, how to do any other useful things that I have forgotten
about...

Zdenek