[llvm-symbolizer] Add support for --basenames/-s

This fixes https://bugs.llvm.org/show_bug.cgi?id=40068.

--basenames is a GNU addr2line switch which strips the directory names
from the file path in the output.

Reviewed by: ruiu

Differential Revision: https://reviews.llvm.org/D56919

llvm-svn: 351795
diff --git a/llvm/docs/CommandGuide/llvm-symbolizer.rst b/llvm/docs/CommandGuide/llvm-symbolizer.rst
index 5699920..bfe8f3e 100644
--- a/llvm/docs/CommandGuide/llvm-symbolizer.rst
+++ b/llvm/docs/CommandGuide/llvm-symbolizer.rst
@@ -119,6 +119,10 @@
  Print human readable output. If ``-inlining`` is specified, enclosing scope is
  prefixed by (inlined by). Refer to listed examples.
 
+.. option:: -basenames, -s
+
+ Strip directories when printing the file path.
+
 EXIT STATUS
 -----------