gcc-4.8: add library paths reported by system linker

[svenpeter42]

Right now only part of the system's libc is symlinked into the conda env - namely the startup files crtXXX.o.
In addition the path to the actual shared object libc.so also needs to be added to the spec file in case a custom
linker is used inside the conda env (e.g. because binutils is requested).

This fixes the following error I get when I conda build a package that requires both gcc-4.8 and binutils:
/home/speter/miniconda2/envs/_build/bin/ld: cannot find -lc collect2: error: ld returned 1 exit status Installation failed: gcc is not able to compile a simple 'Hello, World' program.

cc @stuarteberg

[stuarteberg]

Using the full path to the system /usr/bin/ld instead of ld is a good idea. (It avoids problems if the user has a custom install of binutils.) While you're at it, can you also fix the call to ld on line 49, above?

[stuarteberg]

You should bump the build number.

[stuarteberg]

LGTM.

[stuarteberg]

@frol: Just in case it matters for your gcc-5 package -- @svenpeter42 discovered that the gcc-4.8 post-link.sh script doesn't work properly if the user has also installed binutils via conda. This PR fixes it, so I guess it should also be added to gcc-5, if you're still maintaining that recipe. (At the moment, there is no "official" binutils package from conda, so this will only affect a very small minority of users.)

If you're not still maintaining the gcc-5 recipe, then sorry for the spam. :-)

[ccordoba12]

Pinging @mingwandroid about this one.

[frol]

Thank you for pinging me! I do still maintain gcc-5 package (and also gcc-6) as well as I maintain conda-forge/binutils feedstock.

[ostrokach]

Is anything holding back this PR? I just spent half a day tring to figure out why conda's gcc / mpich was giving me an error ld: cannot find -lc:

$ mpicc -o mpi_hello_world mpi_hello_world.c
/home/{username}/anaconda/envs/{projectname}/bin/ld: cannot find -lc
collect2: error: ld returned 1 exit status

unless I specified -L/usr/lib/x86_64-linux-gnu.