[patch, fortran] PR18428: use libcpp for preprocessing (review of C/C++ and fortran maintainers needed)

[Dominique Dhumieres]

Another bootstrap failure on Darwin:

...
/opt/gcc/i686-darwin/./prev-gcc/xgcc -B/opt/gcc/i686-darwin/./prev-gcc/ -B/opt/gcc/gcc4.4w/i686-apple-darwin9/bin/ -c  -g -O2 -fomit-frame-pointer -DIN_GCC   -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition -Wmissing-format-attribute -pedantic -Wno-long-long -Wno-variadic-macros                                      -Wno-overlength-strings -Werror -fno-common  -DHAVE_CONFIG_H -I. -Ifortran -I../../gcc-4.4-work/gcc -I../../gcc-4.4-work/gcc/fortran -I../../gcc-4.4-work/gcc/../include -I./../intl -I../../gcc-4.4-work/gcc/../libcpp/include -I/sw/include  -I../../gcc-4.4-work/gcc/../libdecnumber -I../../gcc-4.4-work/gcc/../libdecnumber/dpd -I../libdecnumber  -DBASEVER="\"4.4.0\"" \
                ../../gcc-4.4-work/gcc/fortran/cpp.c -o fortran/cpp.o
cc1: warnings being treated as errors
../../gcc-4.4-work/gcc/fortran/cpp.c: In function 'cpp_define_builtins':
../../gcc-4.4-work/gcc/fortran/cpp.c:222: error: implicit declaration of function 'darwin_cpp_builtins'
make[3]: *** [fortran/cpp.o] Error 1
make[3]: *** Waiting for unfinished jobs....
rm gcj-dbtool.pod fsf-funding.pod jcf-dump.pod jv-convert.pod grmic.pod gcov.pod gcj.pod gc-analyze.pod gfdl.pod cpp.pod gij.pod gfortran.pod gcc.pod
make[2]: *** [all-stage2-gcc] Error 2
make[1]: *** [stage2-bubble] Error 2
make: *** [all] Error 2

TIA

Dominique