Expose wrapped_clang_pp in osx crosstool for ObjC++

Problem:
- When you're using the osx crosstool, compilation of ObjC++ does not work because `wrapped_clang_pp` is not exposed.

Solution:
- Expose `wrapped_clang_pp` in the osx toolchain.

Closes #3270.

PiperOrigin-RevId: 164004043
diff --git a/tools/osx/crosstool/BUILD.tpl b/tools/osx/crosstool/BUILD.tpl
index 8f53767..e82dad2 100644
--- a/tools/osx/crosstool/BUILD.tpl
+++ b/tools/osx/crosstool/BUILD.tpl
@@ -38,6 +38,7 @@
           ":libtool",
           ":make_hashed_objlist.py",
           ":wrapped_clang",
+          ":wrapped_clang_pp",
           ":wrapped_ar",
           ":xcrunwrapper.sh",
         ],