guile-zlib: fix path to zlib

- add patch changing path to `libz.so` from `libdir` to `sharedlibdir`
variable from `zlib.pc`

In `guile-zlib` default way of finding `libz.so` is to load `zlib.pc`
with `PKG_CHECK_MODULES` macro and take path from `libdir` variable
inside.

After change in:
https://www.github.com/NixOS/nixpkgs/pull/476830
ff59162e82
`libdir` variable in `zlib.pc` points to `zlib.static`, so only `libz.a`
is there.
Add patch fixing `configure.ac` to load path from `sharedlibdir` instead.

Fixes build failure of `guile-zlib`:
```
make  check-TESTS
make[1]: Entering directory '/build/source'
make[2]: Entering directory '/build/source'
make[2]: *** [Makefile:873: tests/zlib.log] Error 1
make[2]: Leaving directory '/build/source'
make[1]: *** [Makefile:856: check-TESTS] Error 2
make[1]: Leaving directory '/build/source'
make: *** [Makefile:1059: check-am] Error 2
```

zlib.log:
```
Backtrace:
          19 (primitive-load-path "tests/zlib.scm")
...
In unknown file:
           2 (primitive-load-path "zlib" #<procedure 7fffeee418c0 at
ice-9/boot-9.scm:3603:37 ()>)
In zlib.scm:
   486:25  1 (_)
   486:25  0 (_)

zlib.scm:486:25: Wrong type to apply: #f
```

pkgs/by-name/gu/guile-zlib/guile-zlib-change-zlib-path-from-libdir-to-sharedlibdir.diff

@@ -0,0 +1,12 @@
+diff --git a/configure.ac b/configure.ac
+--- a/configure.ac
++++ b/configure.ac
+@@ -30,7 +30,7 @@ fi
+ 
+ PKG_CHECK_MODULES([LIBZ], [zlib])
+ AC_MSG_CHECKING([libz library directory])
+-PKG_CHECK_VAR([LIBZ_LIBDIR], [zlib], [libdir])
++PKG_CHECK_VAR([LIBZ_LIBDIR], [zlib], [sharedlibdir])
+ AC_MSG_RESULT([$LIBZ_LIBDIR])
+ AS_IF([test "x$LIBZ_LIBDIR" = "x"], [
+   AC_MSG_FAILURE([Unable to identify libz lib path.])

pkgs/by-name/gu/guile-zlib/package.nix

@@ -21,6 +21,11 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-aaZhwHimQq408DNtHy442kh/EYdRdxP0Z1tQGDKmkmc=";
   };
 
+  patches = [
+    # fix path to libz.so to sharedlibdir from zlib.pc
+    ./guile-zlib-change-zlib-path-from-libdir-to-sharedlibdir.diff
+  ];
+
   strictDeps = true;
   nativeBuildInputs = [
     autoreconfHook