If the same file is specified more than once as an input file,
llvm-lib should ignore all but the first occurrence of the file.

RUN: rm -rf %t
RUN: mkdir -p %t

RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o %t/foo.o %S/Inputs/a.s
RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o %t/bar.o %S/Inputs/b.s
RUN: llvm-lib -out:%t/foo.lib %t/foo.o %t/foo.o %t/bar.o

RUN: llvm-ar t %t/foo.lib | FileCheck %s
CHECK: foo.o
CHECK-NOT: foo.o
CHECK: bar.o