This replaces '[%Sx%O(x+1)]'.

* This also resolves an out-of-bounds access when a '#' is encountered.
* This also corrects a wrong format specifier in a panic message in the x86 backend.

be: Panic, if the register constraint, for which a register requirement should be generated, does not allow any registers.

This gives a slightly better diagnostic message than failing to allocate a register later on.

Now we get a nice abort instead of silently generating invalid code, when a sparc immediate constraint cannot be fulfilled.

This enables matching Address+Const.

Other backends can use this, too.
This also corrects the bug, that for Address+Const immediates the check, whether it is a tls entity, was missing.

cleanup: Move the implementation of bitset_fprint() into .c, to not spill #include "irprintf.h" everywhere.

This has not been used for years and the code is often causing compile
problems on systems with bad posix implementations like windows.

'A' is for 5-bit immediates, but the code matches the behavior of 'i', i.e. any immediate.

Instead of having a generaic main loop in be_main with several callbacks
into the targets, split the code in be_main up into a set of convenience
functions and let the targets implement the main loop itself. This is
nicer because:

- The control flow into and out of the functions in the target becomes
  obvious as no external party is using callbacks anymore.
- Targets can insert custom code at any place between the generic
  passes.
- In the future we can parameterize the generic backend passes directly
  instead of stuffing info into generic isa_if structures.

Matze's cleanup broke things 8ebe31d226843d6f2cdfcc1ee100ca607c79ba65
Apparently, value==result shall be explicitly allowed, but in the case
of NaN, result was modified and afterwards a read from value returns the
wrong results. Fix was to move the reads before the writes.

Also, a cast from implicit one to explicit one forgot to set the one.
Likewise, the size comparison was oblivious of explicit ones.

Adds few more asserts.

Adds a unittest to check NaN payload stuff.

The optimization was disabled by 8e35902f.

It is only passed around recursively.

This makes the code a bit clearer.