[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.

 --- gdb-6.1.1-dist/readline/configure	2003-05-27 18:29:47.000000000 -0500

 +++ gdb-6.1.1/readline/configure	2004-08-09 14:20:23.000000000 -0500

 @@ -6249,7 +6249,12 @@

  echo "$as_me:$LINENO: checking for mbstate_t" >&5

 +echo $ECHO_N "bash_cv_have_mbstate_t=$bash_cv_have_mbstate_t" >&6

  echo $ECHO_N "checking for mbstate_t... $ECHO_C" >&6

 +if test "${bash_cv_have_mbstate_t+set}" != set; then

 +  bash_cv_have_mbstate_t=yes

 +  echo $ECHO_N "WARNING!! forcing to yes!!! $ECHO_C" >&6

 +fi

  if test "${bash_cv_have_mbstate_t+set}" = set; then

    echo $ECHO_N "(cached) $ECHO_C" >&6

  else