[complib:mpfr] Fix building MPFR in some weird cases

The tmul test uses a compiled-in input file in $(srcdir).
The problem is that the Makefile passes it unquoted. The C code
tries to stringify it using clever macros, which may *usually* work.

In my case the source directory was named:
.../toolchain-powerpc-e500v2-linux-gnuspe-1.0-2.fc10/.../tests
And guess what? During testing I found out the program fails because
it tries to open:
.../toolchain-powerpc-e500v2-1-gnuspe-1.0-2.fc10/.../tests

Yes, CPP tokenized the macro before stringifying it and not surprisingly
the 'linux' part was converted to 1.
[on Fedora-10: cpp (GCC) 4.3.2 20081105 (Red Hat 4.3.2-7)]

So the attached patch simplify the macros and pass the path as string
from the Makefile.

 This is a somewhat ordered TODO list:

 Recuring tasks:

 - update versions for every tools...

 Non-recurring tasks:

 - uClinux

 - add newlib (for enhanced bare metal)

   - may need heavy tweaks and bends in gcc.sh

   - try to make it generic, will help for uClibc++

   - check whether it supports running under uClinux

 - uClibc++

   - see newlib, above

 - Cygwin target (needs newlib)

   - so we can complie for Windows/Cygwin

 - mingw32 target

   - so we can compile for Windows/Win32

 - mingw32 host

   - so we can run natively under Windows/Win32 (without requiring Cygwin)

 - eglibc config file

   - see: http://sourceware.org/ml/crossgcc/2009-05/msg00022.html

 - multilib