[llvm-nm] Simplify. NFC
[llvm-nm] Simplify. NFC

Change a \t to spaces
Change some zero-filling memcpy to aggregate initialization
Delete redundant ArchiveName.clear() after declaration

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@345367 91177308-0d34-0410-b5e6-96231b3b80d8

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