Add util/read_symbols.go

- Add util/read_symbols.go to read exported symbols from an AR
  file for use with the symbol prefixing feature
- Move util/fipstools/fipscommon/ar.go -> util/ar/ar.go
- util/ar/ar.go: Support BSD-style AR files

Change-Id: I171b3b952e69c4b87ac04751b7dba3ea9bc2504e
Reviewed-on: https://boringssl-review.googlesource.com/32024
Reviewed-by: David Benjamin <davidben@google.com>

util/fipstools/delocate/delocate.go

diff --git a/util/fipstools/delocate/delocate.go b/util/fipstools/delocate/delocate.go
index a8c4fd0..4734285 100644
--- a/util/fipstools/delocate/delocate.go
+++ b/util/fipstools/delocate/delocate.go
@@ -26,6 +26,7 @@
 	"strconv"
 	"strings"
 
+	"boringssl.googlesource.com/boringssl/util/ar"
 	"boringssl.googlesource.com/boringssl/util/fipstools/fipscommon"
 )
 
@@ -1425,7 +1426,7 @@
 			}
 			defer arFile.Close()
 
-			ar, err := fipscommon.ParseAR(arFile)
+			ar, err := ar.ParseAR(arFile)
 			if err != nil {
 				return err
 			}