Remove more duplicated flags and dependencies

All the stats below are for a hikey960-eng build on AOSP master.

Number of order-only inputs in out/soong/build.ninja:
Before: 2847162
After:   606508

Size of:                       Before  After
out/soong/build.ninja          572MB   233MB  -59%
out/soong/Android-hikey960.mk   15MB     9MB  -40%
out/build-hikey960.ninja       367MB   358MB   -2%

Ninja time in `m nothing`:
Before: 6.9s
After:  5.0s

Soong generation time:
Before: 11.6s
After:   6.6s

Test: m nothing
Test: wrote script that counted inputs, only duplicates were removed
Test: treehugger
Change-Id: I6b7c5ef5b1395014b7bf5fd0b8112d42bee127bf

cc/cc.go

@@ -1138,6 +1138,13 @@ func (c *Module) depsToPaths(ctx android.ModuleContext) PathDeps {
 
 	// Dedup exported flags from dependencies
 	depPaths.Flags = firstUniqueElements(depPaths.Flags)
+	depPaths.GeneratedHeaders = android.FirstUniquePaths(depPaths.GeneratedHeaders)
+	depPaths.ReexportedFlags = firstUniqueElements(depPaths.ReexportedFlags)
+	depPaths.ReexportedFlagsDeps = android.FirstUniquePaths(depPaths.ReexportedFlagsDeps)
+
+	if c.sabi != nil {
+		c.sabi.Properties.ReexportedIncludeFlags = firstUniqueElements(c.sabi.Properties.ReexportedIncludeFlags)
+	}
 
 	return depPaths
 }