Add partialcompileclean phony

When SOONG_USE_PARTIAL_COMPILE transitions from on to off, we need to
remove all files that may have been built using partial compile.

Bug: b/396145326
Test: manual, TH
Change-Id: I1d91f95883fd8b1d92731a490244a898f25e614d
diff --git a/ui/build/build.go b/ui/build/build.go
index 95d7831..781ca18 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -401,6 +401,7 @@
 		if what&RunKati != 0 {
 			installCleanIfNecessary(ctx, config)
 		}
+		partialCompileCleanIfNecessary(ctx, config)
 		runNinjaForBuild(ctx, config)
 		updateBuildIdDir(ctx, config)
 	}