Fix several warnings

A small, nonexhaustive set of warning fixes. The DiscIO Volume change
is a workaround for a GCC bug [1] that causes returning an unengaged
std::optional to emit annoying -Wmaybe-uninitialized warnings.
This last change alone fixes pages upon pages of warnings since
Volume.h is included from several files.

-Wstringop-truncation is another irrelevant warning for us, but
unfortunately there seems to be no way to disable it without
adding ugly pragmas wherever the warning appears.

1 files changed, 1 insertions, 1 deletions

diff --git a/Source/Core/Common/Config/Config.cpp b/Source/Core/Common/Config/Config.cpp
index b65b1d6fad..4d172ae9c2 100644
--- a/Source/Core/Common/Config/Config.cpp
+++ b/Source/Core/Common/Config/Config.cpp
@@ -35,7 +35,7 @@ using ReadLock = std::shared_lock<std::shared_mutex>;
 using WriteLock = std::unique_lock<std::shared_mutex>;
 #endif
 
-void AddLayerInternal(std::shared_ptr<Layer> layer)
+static void AddLayerInternal(std::shared_ptr<Layer> layer)
 {
   {
     WriteLock lock(s_layers_rw_lock);