Improve helpers.h

Use C11 standard _Noreturn instead of attributes (except, of course, MSVC)
Remove unused helpers
Avoid trapping in release builds, in favor of just unreachability
Improve shim when __builtin_* are not available

src/link/assign.c

@@ -439,7 +439,7 @@ void assign_AssignSections(void)
 			return;
 	}
 
-	trap_;
+	unreachable_();
 }
 
 void assign_Cleanup(void)

src/link/main.c

@@ -99,7 +99,7 @@ void error(struct FileStackNode const *where, uint32_t lineNo, char const *fmt,
 		nbErrors++;
 }
 
-noreturn_ void fatal(struct FileStackNode const *where, uint32_t lineNo, char const *fmt, ...)
+_Noreturn void fatal(struct FileStackNode const *where, uint32_t lineNo, char const *fmt, ...)
 {
 	va_list ap;
 

src/link/script.c

@@ -318,7 +318,7 @@ static void processCommand(enum LinkerScriptCommand command, uint16_t arg,
 {
 	switch (command) {
 	case COMMAND_INVALID:
-		trap_;
+		unreachable_();
 
 	case COMMAND_ORG:
 		break;
@@ -391,12 +391,12 @@ struct SectionPlacement *script_NextSection(void)
 
 		switch (parserState) {
 		case PARSER_FIRSTTIME:
-			trap_;
+			unreachable_();
 
 		case PARSER_LINESTART:
 			switch (token->type) {
 			case TOKEN_INVALID:
-				trap_;
+				unreachable_();
 
 			case TOKEN_EOF:
 				if (!popFile())

src/link/section.c

@@ -108,7 +108,7 @@ static void mergeSections(struct Section *target, struct Section *other, enum Se
 		break;
 
 	case SECTION_NORMAL:
-		trap_;
+		unreachable_();
 	}
 
 	other->nextu = target->nextu;