[llvm-symbolizer] Add -C as a short alias to -demangle

Summary: Provides -C as alias to -demangle. Motivation: https://bugs.llvm.org/show_bug.cgi?id=40069.

Reviewers: jhenderson, ruiu, rnk, fjricci

Reviewed By: jhenderson, ruiu

Subscribers: rupprecht, erik.pilkington, llvm-commits

Differential Revision: https://reviews.llvm.org/D56591

llvm-svn: 351300
diff --git a/llvm/docs/CommandGuide/llvm-symbolizer.rst b/llvm/docs/CommandGuide/llvm-symbolizer.rst
index 1b8986d..3c7a26e 100644
--- a/llvm/docs/CommandGuide/llvm-symbolizer.rst
+++ b/llvm/docs/CommandGuide/llvm-symbolizer.rst
@@ -83,7 +83,7 @@
  Prefer function names stored in symbol table to function names
  in debug info sections. Defaults to true.
 
-.. option:: -demangle
+.. option:: -demangle, -C
 
  Print demangled function names. Defaults to true.