Add --sort-common to the man page.

Differential Revision: https://reviews.llvm.org/D62799

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@362354 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ld.lld.1 b/docs/ld.lld.1
index 1a2fe61..b398c19 100644
--- a/docs/ld.lld.1
+++ b/docs/ld.lld.1
@@ -429,6 +429,8 @@
 .Dv DT_SONAME
 to
 .Ar value .
+.It Fl -sort-common
+This option is ignored for GNU compatibility.
 .It Fl -sort-section Ns = Ns Ar value
 Specifies sections sorting rule when linkerscript is used.
 .It Fl -start-lib