Document that we recommend to turn off -gmodules when building a static

library for distribution to other machines on the clang man page.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@256287 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CommandGuide/clang.rst

@@ -262,7 +262,12 @@ Code Generation Options
   Generate debug information that contains external references to
   types defined in clang modules or precompiled headers instead of
   emitting redundant debug type information into every object file.
-  This option implies `-fmodule-format=obj`.
+  This option implies :option:`-fmodule-format=obj`.
+
+  This option should not be used when building static libraries for
+  distribution to other machines because the debug info will contain
+  references to the module cache on the machine the object files in
+  the library were built on.
   
 .. option:: -fstandalone-debug -fno-standalone-debug