Update version_script.lds and exported_symbols.lds to include all of absl in the produced library. (#156)

diff --git a/cc/exported_symbols.lds b/cc/exported_symbols.lds
index d74d230..e6ccbbd 100644
--- a/cc/exported_symbols.lds
+++ b/cc/exported_symbols.lds
@@ -1 +1,2 @@
 *tink*
+*absl*
diff --git a/cc/version_script.lds b/cc/version_script.lds
index d1b56f5..385cd72 100644
--- a/cc/version_script.lds
+++ b/cc/version_script.lds
@@ -1,6 +1,7 @@
 VERS_1.2 {
   global:
     *tink*;
+    *absl*;
   local:
     *;
 };