[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.

 # dmalloc debug facility

 config DEBUG_dmalloc

     bool

 choice

     bool

     prompt "dmalloc version"

 config DMALLOC_V_5_4_3

     bool

     prompt "5.4.3 (OBSOLETE)"

     depends on OBSOLETE

 config DMALLOC_V_5_5_2

     bool

     prompt "5.5.2"

 # CT_INSERT_VERSION_ABOVE

 # Don't remove above line!

 endchoice

 config DMALLOC_VERSION

     string

     default "5.4.3" if DMALLOC_V_5_4_3

     default "5.5.2" if DMALLOC_V_5_5_2

 # CT_INSERT_VERSION_STRING_ABOVE

 # Don't remove above line!