Globally suppress -Wmaybe-uninitialized

We have needed to suppress it in a bunch of places because GCC has kept
giving false positives depending on optimization settings. When I noticed
yet another false positive when I attempted to build the game with PGO
profiling data using CMake, it was the last straw.

Let's just suppress the warning globally and move on with our lives.

CMakeLists.txt

@@ -295,6 +295,14 @@ check_compiler_has_flag(
 	"-Wno-literal-suffix"
 )
 
+# This flag is too aggressive and keeps giving false positives.
+check_compiler_has_flag(
+	CXX_FLAGS_STRICT_COMPILATION
+	"-Wmaybe-uninitialized"
+	HAS_COMPILER_FLAG_WMAYBE_UNINITIALIZED
+	"-Wno-maybe-uninitialized"
+)
+
 # This removes a lot of warnings from Clang regarding unused -I arguments
 check_compiler_has_flag(
 	CXX_FLAGS_STRICT_COMPILATION

SConstruct

@@ -474,7 +474,7 @@ for env in [test_env, client_env, env]:
             env.AppendUnique(CXXFLAGS = ["-fopenmp"], LIBS = ["gomp"])
 
         if env['strict']:
-            env.AppendUnique(CCFLAGS = Split("-Werror $(-Wno-unused-local-typedefs$)"))
+            env.AppendUnique(CCFLAGS = Split("-Werror $(-Wno-unused-local-typedefs$) $(-Wno-maybe-uninitialized$)"))
             env.AppendUnique(CXXFLAGS = Split("-Wold-style-cast"))
         if env['sanitize']:
             env.AppendUnique(CCFLAGS = ["-fsanitize=" + env["sanitize"]], LINKFLAGS = ["-fsanitize=" + env["sanitize"]])

src/gui/widgets/listbox.cpp

@@ -332,17 +332,6 @@ bool listbox::update_content_size()
 	return false;
 }
 
-/* Suppress -Wmaybe-uninitialized warnings.
- * @GregoryLundberg reported in IRC that GCC 6.2.1 with SCons gives a warning that the value
- * of horizontal_scrollbar_position can be used uninitialized. It's of course not possible
- * (boost::optional conversion to bool returns true only if the value is set), but GCC can't
- * prove that to itself.
- */
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
-
 void listbox::place(const point& origin, const point& size)
 {
 	boost::optional<unsigned> vertical_scrollbar_position, horizontal_scrollbar_position;
@@ -375,10 +364,6 @@ void listbox::place(const point& origin, const point& size)
 	}
 }
 
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
-
 void listbox::resize_content(const int width_modification,
 		const int height_modification,
 		const int width_modification_pos,

src/lexical_cast.hpp

@@ -124,16 +124,6 @@ struct bad_lexical_cast : std::exception
 
 namespace implementation {
 
-/* Suppress -Wmaybe-uninitialized warnings.
- * I (Jyrki) noticed that building with -Og on my system (GCC 7.2.0, Boost 1.61)
- * GCC may omit a warning that the value of `fallback` may be used uninitialized.
- * It's impossible, but GCC can't prove that to itself.
- */
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
-
 /**
  * Base class for the conversion.
  *
@@ -495,10 +485,6 @@ struct lexical_caster<
 	}
 };
 
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
-
 } // namespace implementation
 
 #endif

src/scripting/game_lua_kernel.cpp

@@ -131,13 +131,6 @@ class CVideo;
 #include "scripting/debug_lua.hpp"
 #endif
 
-// Suppress uninitialized variables warnings, because of boost::optional constructors in this file which apparently confuses gcc
-#if defined(__GNUC__) && !defined(__clang__) // we shouldn't need this for clang, but for gcc and tdm-gcc we probably do
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6 ) // "GCC diagnostic ignored" is apparently not available at version 4.5.2
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
-#endif
-
 static lg::log_domain log_scripting_lua("scripting/lua");
 #define LOG_LUA LOG_STREAM(info, log_scripting_lua)
 #define WRN_LUA LOG_STREAM(warn, log_scripting_lua)

src/xBRZ/xbrz.cpp

@@ -43,12 +43,6 @@
 
 #include "utils/functional.hpp"
 
-#if defined(__GNUC__) && !defined(__clang__) && !defined(__WIN32__) // We only want this for gcc, not clang or tdm-gcc
-#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ <= 8 )
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"               //Suppress uninitialized variables warnings on GCC <= 4.8.x
-#endif
-#endif
-
 namespace
 {
 template <uint32_t N> inline