*: add "noexcept" to many, many function prototypes

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

test/test_translate_song.cxx

@@ -32,7 +32,7 @@ Log(const Domain &domain, gcc_unused LogLevel level, const char *msg)
 }
 
 bool
-uri_supported_scheme(const char *uri)
+uri_supported_scheme(const char *uri) noexcept
 {
 	return strncmp(uri, "http://", 7) == 0;
 }
@@ -130,13 +130,13 @@ DetachedSong::LoadFile(Path path)
 }
 
 const Database *
-Client::GetDatabase() const
+Client::GetDatabase() const noexcept
 {
 	return reinterpret_cast<const Database *>(this);
 }
 
 const Storage *
-Client::GetStorage() const
+Client::GetStorage() const noexcept
 {
 	return ::storage;
 }