Be even more C++. Switch on a warning.

Remove lots of "extern C" and "ifdef __cplusplus" which are no longer
needed now all of vold is C++. Also turn on the cert-err58-cpp warning
we once had to disable.

Bug: 67041047
Test: compiles, boots
Change-Id: I8c6f9dd486f2409e0deed7bb648d959677465b21
diff --git a/cryptfs.cpp b/cryptfs.cpp
index ae9b0af..7302c44 100644
--- a/cryptfs.cpp
+++ b/cryptfs.cpp
@@ -2051,6 +2051,11 @@
     return rc;
 }
 
+static int vold_unmountAll(void) {
+    VolumeManager* vm = VolumeManager::Instance();
+    return vm->unmountAll();
+}
+
 int cryptfs_enable_internal(const char *howarg, int crypt_type, const char *passwd,
                             int no_ui)
 {