[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.

 reporter_name="Nate CASE"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00016.html"

 reporter_comment="This is a sample config file for Freescale e500v2 processors (e.g.,

 MPC8548, MPC8572).  It uses eglibc (for e500/SPE patches) and a recent

 gcc (4.3.1, for e500v2 DPFP support) and will generate appropriate

 dual-precision floating point instructions by default.

 Note: If building a Linux kernel with this toolchain, you will want to

 make sure -mno-spe AND -mspe=no are passed to gcc to prevent SPE

 ABI/instructions from getting into the kernel (which is currently

 unsupported).  At this time, the kernel build system only passes

 -mno-spe by default (this should be fixed soon hopefully)."