fix build number for binutils

[h-vetinari]

I was diffing build environments in a build that started failing without any relevant changes, and saw

     binutils_impl_linux-64:               2.40-ha1999f0_7            conda-forge
-    binutils_linux-64:                    2.40-hb3c18ed_9            conda-forge
+    binutils_linux-64:                    2.40-hb3c18ed_0            conda-forge

meaning that a build 2 month ago pulled in _9, while today I got _0 (and the impl package didn't change).

As it turns out #121 reset the build number to 0, because there was no separate build number for binutils. Introduce one so we keep incrementing the build number correctly until a new binutils version comes along.

[conda-forge-webservices]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

[h-vetinari]

Ping @conda-forge/ctng-compiler-activation, this is a trivial fix, PTAL

[isuruf]

Superceded by #133