[LLD] [Docs] explain --unresolved-symbols options (llvm#165937)

Tested with `man lld/docs/ld.lld.1`

Author: fmayer

lld/docs/ld.lld.1

@@ -719,6 +719,19 @@ a given pattern are handled as if they were given as arguments of
 Creates a separate output section for every orphan input section.
 .It Fl -unresolved-symbols Ns = Ns Ar value
 Determine how to handle unresolved symbols.
+.Ar value
+may be:
+.Pp
+.Bl -tag -width 2n -compact
+.It Cm report-all
+Report unresolved symbols (default).
+.It Cm ignore-in-object-files
+Only report unresolved symbols contained in shared libraries.
+.It Cm ignore-in-shared-libs
+Only report unresolved symbols contained in object files.
+.It Cm ignore-all
+Do not report unresolved symbols.
+.El
 .It Fl -use-android-relr-tags
 Use SHT_ANDROID_RELR / DT_ANDROID_RELR* tags instead of SHT_RELR / DT_RELR*.
 .It Fl v , Fl V