Simple refactoring of prefix related functions.

Rename the two prefix-in-list funcs so that their usages are clearer.
Also find and replace all the code that essentially does either.

This introduces additional loops in some places, but I think the added
readability and simplicity outweighs the performance degradation, which
should be negligible anyway.

Test: m nothing
Test: TreeHugger
Change-Id: I37e2276ca0c815105ed0031f23c0b1264b480e4f
diff --git a/cc/library.go b/cc/library.go
index 0bddab5..bca9a96 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -281,11 +281,9 @@
 }
 
 func (f *flagExporter) reexportFlags(flags ...string) {
-	for _, flag := range flags {
-		if strings.HasPrefix(flag, "-I") || strings.HasPrefix(flag, "-isystem") {
-			panic(fmt.Errorf("Exporting invalid flag %q: "+
-				"use reexportDirs or reexportSystemDirs to export directories", flag))
-		}
+	if android.PrefixInList(flags, "-I") || android.PrefixInList(flags, "-isystem") {
+		panic(fmt.Errorf("Exporting invalid flag %q: "+
+			"use reexportDirs or reexportSystemDirs to export directories", flag))
 	}
 	f.flags = append(f.flags, flags...)
 }