Use standard attribute syntax instead of IBM __attribute__

Move format attrs to proper standard location

For some reason, GCC 13 is more lax than earlier versions...

src/asm/format.cpp

@@ -45,7 +45,7 @@ void FormatSpec::useCharacter(int c) {
 	case '0':
 		if (state < FORMAT_WIDTH)
 			padZero = true;
-		// fallthrough
+		[[fallthrough]];
 	case '1':
 	case '2':
 	case '3':

src/asm/lexer.cpp

@@ -864,7 +864,7 @@ static void discardBlockComment() {
 		case '\r':
 			// Handle CRLF before nextLine() since shiftChar updates colNo
 			handleCRLF(c);
-			// fallthrough
+			[[fallthrough]];
 		case '\n':
 			if (lexerState->expansions.empty())
 				nextLine();
@@ -879,7 +879,7 @@ static void discardBlockComment() {
 				shiftChar();
 				return;
 			}
-			// fallthrough
+			[[fallthrough]];
 		default:
 			continue;
 		}
@@ -1216,7 +1216,7 @@ static void appendEscapedSubstring(std::string &yylval, std::string const &str)
 		case '"':
 		case '{':
 			yylval += '\\';
-			// fallthrough
+			[[fallthrough]];
 		default:
 			yylval += c;
 			break;
@@ -1515,7 +1515,7 @@ static Token yylex_NORMAL() {
 
 		case ';':
 			discardComment();
-			// fallthrough
+			[[fallthrough]];
 		case ' ':
 		case '\t':
 			break;
@@ -1729,7 +1729,7 @@ static Token yylex_NORMAL() {
 
 		case '\r':
 			handleCRLF(c);
-			// fallthrough
+			[[fallthrough]];
 		case '\n':
 			return Token(T_(NEWLINE));
 
@@ -1751,7 +1751,7 @@ static Token yylex_NORMAL() {
 				shiftChar();
 				return Token(T_(STRING), readString(true));
 			}
-			// fallthrough
+			[[fallthrough]];
 
 			// Handle identifiers... or report garbage characters
 
@@ -1846,7 +1846,7 @@ static Token yylex_RAW() {
 		case ';': // Comments inside macro args
 			discardComment();
 			c = peek();
-			// fallthrough
+			[[fallthrough]];
 		case '\r': // End of line
 		case '\n':
 		case EOF:
@@ -1920,7 +1920,7 @@ backslash:
 				error("Illegal character escape %s\n", printChar(c));
 				break;
 			}
-			// fallthrough
+			[[fallthrough]];
 
 		default: // Regular characters will just get copied
 append:

src/asm/main.cpp

@@ -198,7 +198,7 @@ int main(int argc, char *argv[]) {
 		// introduced to better match the `-I dir` option of gcc and clang.
 		case 'i':
 			warning(WARNING_OBSOLETE, "`-i` is deprecated; use `-I`\n");
-			// fallthrough
+			[[fallthrough]];
 		case 'I':
 			fstk_AddIncludePath(musl_optarg);
 			break;

src/asm/section.cpp

@@ -47,7 +47,7 @@ std::optional<std::string> currentLoadScope = std::nullopt;
 int32_t loadOffset; // Offset into the LOAD section's parent (see sect_GetOutputOffset)
 
 // A quick check to see if we have an initialized section
-attr_(warn_unused_result) static bool checksection() {
+[[nodiscard]] static bool checksection() {
 	if (currentSection)
 		return true;
 
@@ -57,7 +57,7 @@ attr_(warn_unused_result) static bool checksection() {
 
 // A quick check to see if we have an initialized section that can contain
 // this much initialized data
-attr_(warn_unused_result) static bool checkcodesection() {
+[[nodiscard]] static bool checkcodesection() {
 	if (!checksection())
 		return false;
 
@@ -71,7 +71,7 @@ attr_(warn_unused_result) static bool checkcodesection() {
 	return false;
 }
 
-attr_(warn_unused_result) static bool checkSectionSize(Section const &sect, uint32_t size) {
+[[nodiscard]] static bool checkSectionSize(Section const &sect, uint32_t size) {
 	uint32_t maxSize = sectionTypeInfo[sect.type].size;
 
 	// If the new size is reasonable, keep going
@@ -88,7 +88,7 @@ attr_(warn_unused_result) static bool checkSectionSize(Section const &sect, uint
 }
 
 // Check if the section has grown too much.
-attr_(warn_unused_result) static bool reserveSpace(uint32_t delta_size) {
+[[nodiscard]] static bool reserveSpace(uint32_t delta_size) {
 	// This check is here to trap broken code that generates sections that are too big and to
 	// prevent the assembler from generating huge object files or trying to allocate too much
 	// memory.