build: Turn on more warning flags

-Wshadow these days does not overwarn anymore like it did in gcc 4.
There are no warnings inside gtk, so better enable it to keep it that
way.

-Wuninitialized also has no positives, so I'm gonna turn it on just
because.

meson.build

@@ -247,8 +247,6 @@ elif cc.get_id() == 'gcc' or cc.get_id() == 'clang'
     '-Wmissing-format-attribute',
     '-Wmissing-include-dirs',
     '-Wlogical-op',
-    '-Wno-uninitialized',
-    '-Wno-shadow',
     '-Werror=redundant-decls',
     '-Werror=implicit',
     '-Werror=nonnull',