[C] Suppress maybe-uninitialized warnings in GCC.

GCC is known to emit false positives when it cannot detect if a variable
is initialized.

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/c/CGenerator.java

@@ -309,8 +309,15 @@ private static void generateGroupHeaderFunctions(
             "    {\n" +
             "        return NULL;\n" +
             "    }\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic push\n" +
+            "#pragma GCC diagnostic ignored \"-Wmaybe-uninitialized\"\n" +
+            "#endif\n" +
             "    %5$s_set_blockLength(&codec->dimensions, (%2$s)%3$d);\n" +
             "    %5$s_set_numInGroup(&codec->dimensions, (%4$s)count);\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic pop\n" +
+            "#endif\n" +
             "    codec->index = -1;\n" +
             "    codec->count = count;\n" +
             "    codec->block_length = %3$d;\n" +
@@ -337,7 +344,14 @@ private static void generateGroupHeaderFunctions(
 
             "SBE_ONE_DEF uint64_t %3$s_sbe_position(const struct %3$s *const codec)\n" +
             "{\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic push\n" +
+            "#pragma GCC diagnostic ignored \"-Wmaybe-uninitialized\"\n" +
+            "#endif\n" +
             "    return *codec->position_ptr;\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic pop\n" +
+            "#endif\n" +
             "}\n\n" +
 
             "SBE_ONE_DEF bool %3$s_set_sbe_position(struct %3$s *const codec, const uint64_t position)\n" +
@@ -358,14 +372,28 @@ private static void generateGroupHeaderFunctions(
 
             "SBE_ONE_DEF bool %3$s_has_next(const struct %3$s *const codec)\n" +
             "{\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic push\n" +
+            "#pragma GCC diagnostic ignored \"-Wmaybe-uninitialized\"\n" +
+            "#endif\n" +
             "    return codec->index + 1 < codec->count;\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic pop\n" +
+            "#endif\n" +
             "}\n\n" +
 
             "SBE_ONE_DEF struct %3$s *%3$s_next(struct %3$s *const codec)\n" +
             "{\n" +
             "    codec->offset = *codec->position_ptr;\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic push\n" +
+            "#pragma GCC diagnostic ignored \"-Wmaybe-uninitialized\"\n" +
+            "#endif\n" +
             "    if (SBE_BOUNDS_CHECK_EXPECT(((codec->offset + codec->block_length) " +
             "> codec->buffer_length), false))\n" +
+            "#if defined(__GNUG__) && !defined(__clang__)\n" +
+            "#pragma GCC diagnostic pop\n" +
+            "#endif\n" +
             "    {\n" +
             "        errno = E108;\n" +
             "        return NULL;\n" +