[lld] [llvm] [lld][COFF] Remove duplicate strtab entries (PR #141197)

[Haohai Wen via llvm-commits]

HaohaiWen wrote:

> Blender strtab size for three methods.
> 
> original strtab size	stringmap strtab size	strtabbuilder strtab size
> 630,474,756	373,099,443	342,999,672
> stringmap reduced -40.82% comparing to unoptimized strtab. stringtablebuilder further reduced -8.07%.

strtab size after this PR: 342,999,676


https://github.com/llvm/llvm-project/pull/141197