[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.

Manually backported from 1449:8ad2773e7ae3

 # Compute ARM-specific values

 CT_DoArchTupleValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}${target_endian_eb}"

     # The system part of the tuple:

     case "${CT_LIBC},${CT_ARCH_ARM_EABI}" in

         *glibc,y)   CT_TARGET_SYS=gnueabi;;

         uClibc,y)   CT_TARGET_SYS=uclibcgnueabi;;

         none,y)     CT_TARGET_SYS=eabi;;

     esac

     # In case we're EABI, do *not* specify any ABI!

     # which means, either we do not have an ABI specified, or we're not EABI.

     CT_TestOrAbort "Internal error: CT_ARCH_ABI should not be set for EABI build." -z "${CT_ARCH_ABI}" -o -z "${CT_ARCH_ARM_EABI}"

 }