[llvm-ar] Add some test-cases for empty archives

We had coverage of empty archive in our downstream testsuite.
This adds those cases upstream.

Differential Revision: https://reviews.llvm.org/D107471

llvm/test/tools/llvm-ar/display-empty.test

@@ -0,0 +1,11 @@
+## Test Display of empty archives.
+
+# RUN: rm -rf %t && mkdir -p %t
+
+## Display empty archive:
+# RUN: llvm-ar cr %t/empty.a
+# RUN: llvm-ar tv %t/empty.a 2>&1 | count 0
+
+## Display empty thin archive:
+# RUN: llvm-ar Trc %t/thin-archive-empty.a
+# RUN: llvm-ar tv %t/thin-archive-empty.a 2>&1 | count 0

llvm/test/tools/llvm-ar/print.test

@@ -8,6 +8,11 @@
 
 # RUN: llvm-ar -rc %t/archive.a %t/1.txt %t/2.txt %t/3.txt
 
+## Print empty archive:
+# RUN: llvm-ar cr %t/empty.a
+# RUN: llvm-ar p %t/empty.a 2>&1 | count 0
+# RUN: llvm-ar pv %t/empty.a 2>&1 | count 0
+
 ## Print without member:
 # RUN: llvm-ar p %t/archive.a \
 # RUN:   | FileCheck %s --check-prefix=WITHOUT --match-full-lines --implicit-check-not {{.}}
@@ -83,6 +88,11 @@
 
 # MISSING-FILE: error: '[[FILE]]' was not found
 
+## Print empty thin archive:
+# RUN: llvm-ar Trc %t/thin-archive-empty.a
+# RUN: llvm-ar p %t/thin-archive-empty.a 2>&1 | count 0
+# RUN: llvm-ar pv %t/thin-archive-empty.a 2>&1 | count 0
+
 ## Print thin archive:
 # RUN: llvm-ar Trc %t/thin-archive.a %t/1.txt %t/2.txt %t/3.txt
 # RUN: llvm-ar p %t/archive.a %t/2.txt \