[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.

 # Super-H specific configuration file

 # depends on EXPERIMENTAL

 config ARCH_sh

     select ARCH_USE_MMU

     select ARCH_SUPPORTS_BOTH_ENDIAN

     select ARCH_DEFAULT_LE

     help

       The Super-H architecture, as defined by:

         http://www.renesas.com/fmwk.jsp?cnt=superh_family_landing.jsp&fp=/products/mpumcu/superh_family/

 choice

     bool

     prompt "Variant"

 config ARCH_SH_SH3

     bool

     prompt "sh3"

 config ARCH_SH_SH4

     bool

     prompt "sh4"

 config ARCH_SH_SH4A

     bool

     prompt "sh4a"

 endchoice

 config ARCH_SH_VARIANT

     string

     default "sh3"   if ARCH_SH_SH3

     default "sh4"   if ARCH_SH_SH4

     default "sh4a"  if ARCH_SH_SH4A