Add back grep-includes alias (#888)

There's references to this from bazel https://github.com/bazelbuild/bazel/blob/5604b553b2a54152e5e4f41ef4b01a416b7bfd44/tools/cpp/BUILD.tools#L44

We should remove both but in the meantime some rulesets reference this

Closes #888

COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_cc/pull/888 from keith:ks/add-back-grep-includes-alias ebc21b3f0726853f80f0ebddb898bfd205277870
PiperOrigin-RevId: 992413533
Change-Id: Iaeaf5a245db5a7a8a5fc891d4c70324a4b57f868

cc/private/toolchain/BUILD

diff --git a/cc/private/toolchain/BUILD b/cc/private/toolchain/BUILD
index abd4e6b..e3c0680 100644
--- a/cc/private/toolchain/BUILD
+++ b/cc/private/toolchain/BUILD
@@ -59,6 +59,12 @@
 )
 
 filegroup(
+    name = "grep-includes",
+    srcs = ["empty.cc"],
+    deprecation = "grep-includes is always empty, you must provide your own.",
+)
+
+filegroup(
     name = "empty",
     srcs = [],
 )