[ELF][test] Demonstrate --no-allow-shlib-undefined behavior with a hidden relocatable object file definition

1981b1b improved the check.

Author: MaskRay

lld/test/ELF/allow-shlib-undefined.s

@@ -37,6 +37,17 @@
 # RUN: not ld.lld %t.o %t.so %t2.so -o /dev/null 2>&1 | \
 # RUN:   FileCheck %s --check-prefixes=CHECK,CHECK2
 
+## Test some cases where relocatable object files provide a hidden definition.
+# RUN: echo '.globl _unresolved; _unresolved:' | llvm-mc -filetype=obj -triple=x86_64 -o %tdef.o
+# RUN: echo '.globl _unresolved; .hidden _unresolved; _unresolved:' | llvm-mc -filetype=obj -triple=x86_64 -o %tdef-hidden.o
+# RUN: ld.lld %t.o %t.so %tdef-hidden.o -o /dev/null 2>&1 | count 0
+
+## The section containing the definition is discarded, and we report an error.
+# RUN: not ld.lld --gc-sections %t.o %t.so %tdef-hidden.o -o /dev/null 2>&1 | FileCheck %s
+## The definition %tdef.so is ignored.
+# RUN: ld.lld -shared -soname=tdef.so %tdef.o -o %tdef.so
+# RUN: not ld.lld --gc-sections %t.o %t.so %tdef.so %tdef-hidden.o -o /dev/null 2>&1 | FileCheck %s
+
 .globl _start
 _start:
   callq _shared@PLT