Pass system include dirs to header ABI checker

This commit fixes the incomplete ABI dumps for libc. The ABI checker
counts export_system_include_dir in the exported headers. It writes the
functions and types defined in the system headers to the dump files.

Test: make
Bug: 314010764
Change-Id: Ieae48d13b4fc4381c87a017213019e940d498967
diff --git a/cc/sabi.go b/cc/sabi.go
index af26726..ef43c8d 100644
--- a/cc/sabi.go
+++ b/cc/sabi.go
@@ -92,7 +92,8 @@
 
 	// Include directories that may contain ABI information exported by a library.
 	// These directories are passed to the header-abi-dumper.
-	ReexportedIncludes []string `blueprint:"mutated"`
+	ReexportedIncludes       []string `blueprint:"mutated"`
+	ReexportedSystemIncludes []string `blueprint:"mutated"`
 }
 
 type sabi struct {