gcc-{,cross-}wrapper: add 'cpp' wrapper (close #1820)

The gcc-wrapper doesn't wrap 'cpp'. This breaks some software (such as
Buildroot) because the 'cpp' they get come from the non-wrapped gcc
package which doesn't know about any standard include paths.

gcc-cross-wrapper is untested.

pkgs/build-support/gcc-cross-wrapper/builder.sh

@@ -87,6 +87,8 @@ mkGccWrapper $out/bin/$crossConfig-gcc $gccPath/$crossConfig-gcc
 mkGccWrapper $out/bin/$crossConfig-g++ $gccPath/$crossConfig-g++
 ln -s $crossConfig-g++ $out/bin/$crossConfig-c++
 
+mkGccWrapper $out/bin/$crossConfig-cpp $gccPath/$crossConfig-cpp
+
 mkGccWrapper $out/bin/$crossConfig-g77 $gccPath/$crossConfig-g77
 ln -s $crossConfig-g77 $out/bin/$crossConfig-f77
 

pkgs/build-support/gcc-wrapper/builder.sh

@@ -154,6 +154,8 @@ then
     ln -sv g++ $out/bin/c++
 fi
 
+mkGccWrapper $out/bin/cpp $gccPath/cpp
+
 if mkGccWrapper $out/bin/gfortran $gccPath/gfortran
 then
     ln -sv gfortran $out/bin/g77