tests.srcOnly: Use zlib instead of glibc

This makes the test more portable, as glibc does not evaluate on
all platforms.
Unfortunately the test fails on darwin for an unrelated reason.
__impureHostDeps values were duplicated.

pkgs/build-support/src-only/tests.nix

@@ -3,18 +3,18 @@
   srcOnly,
   hello,
   emptyDirectory,
-  glibc,
+  zlib,
   stdenv,
   testers,
 }:
 
 let
   emptySrc = srcOnly emptyDirectory;
-  glibcSrc = srcOnly glibc;
+  zlibSrc = srcOnly zlib;
 
   # It can be invoked in a number of ways. Let's make sure they're equivalent.
-  glibcSrcDrvAttrs = srcOnly glibc.drvAttrs;
-  # glibcSrcFreeform = # ???;
+  zlibSrcDrvAttrs = srcOnly zlib.drvAttrs;
+  # zlibSrcFreeform = # ???;
   helloSrc = srcOnly hello;
   helloSrcDrvAttrs = srcOnly hello.drvAttrs;
 
@@ -48,11 +48,11 @@ in
 runCommand "srcOnly-tests"
   {
     moreTests = [
-      (testers.testEqualDerivation "glibcSrcDrvAttrs == glibcSrc" glibcSrcDrvAttrs glibcSrc)
+      (testers.testEqualDerivation "zlibSrcDrvAttrs == zlibSrc" zlibSrcDrvAttrs zlibSrc)
       # (testers.testEqualDerivation
-      #   "glibcSrcFreeform == glibcSrc"
-      #   glibcSrcFreeform
-      #   glibcSrc)
+      #   "zlibSrcFreeform == zlibSrc"
+      #   zlibSrcFreeform
+      #   zlibSrc)
       (testers.testEqualDerivation "helloSrcDrvAttrs == helloSrc" helloSrcDrvAttrs helloSrc)
       (testers.testEqualDerivation "helloDrvSimpleSrcFreeform == helloDrvSimpleSrc"
         helloDrvSimpleSrcFreeform
@@ -67,9 +67,9 @@ runCommand "srcOnly-tests"
       exit 1
     fi
 
-    # Test that glibcSrc is not empty
-    if [ -z "$(ls -A ${glibcSrc})" ]; then
-      echo "glibcSrc is empty"
+    # Test that zlibSrc is not empty
+    if [ -z "$(ls -A ${zlibSrc})" ]; then
+      echo "zlibSrc is empty"
       exit 1
     fi