build system: compile without maybe-uninitialized warnings for gcc

See e.g.
http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct

Rakefile

@@ -117,7 +117,7 @@ def setup_globals
   cflags                   = "#{cflags_common} #{c(:USER_CFLAGS)}"
 
   cxxflags                 = "#{cflags_common} #{c(:STD_CXX)}"
-  cxxflags                += " -Wnon-virtual-dtor -Woverloaded-virtual -Wextra -Wno-missing-field-initializers"
+  cxxflags                += " -Wnon-virtual-dtor -Woverloaded-virtual -Wextra -Wno-missing-field-initializers #{c(:WNO_MAYBE_UNINITIALIZED)}"
   cxxflags                += " #{c(:WXWIDGETS_CFLAGS)} #{c(:QT_CFLAGS)} #{c(:BOOST_CPPFLAGS)} #{c(:CURL_CFLAGS)} #{c(:USER_CXXFLAGS)}"
 
   ldflags                  = ""

ac/compiler_flags.m4

@@ -20,8 +20,12 @@ if test x"$ac_cv_compiler_is_clang" = xyes; then
   AC_LANG_POP()
   CXXFLAGS="$ac_save_CXXFLAGS"
 
-elif check_version 4.8.0 $ac_cv_gcc_version ; then
-  WLOGICAL_OP="-Wlogical-op"
+else
+  WNO_MAYBE_UNINITIALIZED="-Wno-maybe-uninitialized"
+
+  if check_version 4.8.0 $ac_cv_gcc_version ; then
+    WLOGICAL_OP="-Wlogical-op"
+  fi
 fi
 
 AC_SUBST(QUNUSED_ARGUMENTS)
@@ -30,3 +34,4 @@ AC_SUBST(WNO_MISMATCHED_TAGS)
 AC_SUBST(WLOGICAL_OP)
 AC_SUBST(WNO_INCONSISTENT_MISSING_OVERRIDE)
 AC_SUBST(WNO_POTENTIALLY_EVALUATED_EXPRESSION)
+AC_SUBST(WNO_MAYBE_UNINITIALIZED)

build-config.in

@@ -118,6 +118,7 @@ VORBIS_LIBS = @VORBIS_LIBS@
 WLOGICAL_OP = @WLOGICAL_OP@
 WNO_INCONSISTENT_MISSING_OVERRIDE = @WNO_INCONSISTENT_MISSING_OVERRIDE@
 WNO_MISMATCHED_TAGS = @WNO_MISMATCHED_TAGS@
+WNO_MAYBE_UNINITIALIZED = @WNO_MAYBE_UNINITIALIZED@
 WNO_POTENTIALLY_EVALUATED_EXPRESSION = @WNO_POTENTIALLY_EVALUATED_EXPRESSION@
 WNO_SELF_ASSIGN = @WNO_SELF_ASSIGN@
 WXWIDGETS_CFLAGS = @WXWIDGETS_CFLAGS@