fix: fix slice init length (#4133)

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**What type of PR is this?**


> Bug fix


**What does this PR do? Why is it needed?**

The intention here should be to initialize a slice with a capacity of
`len(includeSet)` rather than initializing the length of this slice.

The online demo: https://go.dev/play/p/q1BcVCmvidW


**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

go/tools/builders/compilepkg.go

@@ -403,7 +403,7 @@ func compileArchive(
 		for _, hdr := range srcs.hSrcs {
 			includeSet[filepath.Dir(hdr.filename)] = struct{}{}
 		}
-		includes := make([]string, len(includeSet))
+		includes := make([]string, 0, len(includeSet))
 		for inc := range includeSet {
 			includes = append(includes, inc)
 		}