Note impact of -Cstrip on backtraces

It is not always clear to people what the impact of `-Cstrip` options are.
They are a common question on sites like StackOverflow, and sometimes
people even report bugs with "no backtrace" after deliberately mangling
the symbol table. We cannot exhaustively document every permutation, but
we should warn people about common effects.

Author: workingjubilee

Diff for: src/doc/rustc/src/codegen-options/index.md

@@ -553,9 +553,12 @@ Supported values for this option are:
   of MSVC).
 - `debuginfo` - debuginfo sections and debuginfo symbols from the symbol table
   section are stripped at link time and are not copied to the produced binary
-  or separate files.
+  or separate files. This should leave backtraces mostly-intact but may make
+  using a debugger like gdb or lldb ineffectual.
 - `symbols` - same as `debuginfo`, but the rest of the symbol table section is
-  stripped as well if the linker supports it.
+  stripped as well if the linker supports it. On platforms which depend on the
+  binary's symbol table for backtraces, this can affect them so negatively as to
+  make the trace completely incomprehensible.
 
 ## symbol-mangling-version