Use loops instead of tail calls and musttail

gcc 15.2.1 20250813 complains "address of automatic variable can
escape to `musttail` call" from `-Wmaybe-musttail-local-addr`,
and guaranteeing tail-call optimization cross-platform is more
trouble than it's worth.

include/platform.hpp

@@ -60,13 +60,4 @@
 	#define _POSIX_C_SOURCE 200809L
 #endif
 
-// gcc and clang have their own `musttail` attributes for tail recursion
-#if defined(__clang__) && __has_cpp_attribute(clang::musttail)
-	#define MUSTTAIL [[clang::musttail]]
-#elif defined(__GNUC__) && __has_cpp_attribute(gnu::musttail)
-	#define MUSTTAIL [[gnu::musttail]]
-#else
-	#define MUSTTAIL
-#endif
-
 #endif // RGBDS_PLATFORM_HPP

man/rgbasm.5

@@ -154,6 +154,8 @@ of string constants:
 will be expanded in all of
 .Ql DEF({name}) ,
 .Ql DEF {name} EQU/=/EQUS/etc ... ,
+.Ql REDEF {name} EQU/=/EQUS/etc ... ,
+.Ql FOR {name}, ... ,
 .Ql PURGE {name} ,
 and
 .Ql MACRO {name} ,
@@ -1556,6 +1558,8 @@ in the C programming language.
 This expansion is disabled in a few contexts:
 .Ql DEF(name) ,
 .Ql DEF name EQU/=/EQUS/etc ... ,
+.Ql REDEF name EQU/=/EQUS/etc ... ,
+.Ql FOR name, ... ,
 .Ql PURGE name ,
 and
 .Ql MACRO name

src/asm/lexer.cpp

@@ -716,6 +716,7 @@ int LexerState::peekCharAhead() {
 static std::pair<Symbol const *, std::shared_ptr<std::string>> readInterpolation(size_t depth);
 
 static int peek() {
+	for (;;) {
 		int c = lexerState->peekChar();
 
 		if (lexerState->expansionScanDistance > 0) {
@@ -732,7 +733,6 @@ static int peek() {
 			if (!isMacroChar(lexerState->peekCharAhead())) {
 				return c;
 			}
-
 			// If character is a macro arg char, do macro arg expansion
 			shiftChar();
 			if (std::shared_ptr<std::string> str = readMacroArg(); str) {
@@ -743,20 +743,19 @@ static int peek() {
 				// https://en.wikipedia.org/wiki/Painted_blue
 				lexerState->expansionScanDistance += str->length();
 			}
-
-		MUSTTAIL return peek();
+			// Continue in the next iteration
 		} else if (c == '{') {
 			// If character is an open brace, do symbol interpolation
 			shiftChar();
 			if (auto interp = readInterpolation(0); interp.first && interp.second) {
 				beginExpansion(interp.second, interp.first->name);
 			}
-
-		MUSTTAIL return peek();
+			// Continue in the next iteration
 		} else {
 			return c;
 		}
 	}
+}
 
 static void shiftChar() {
 	if (lexerState->capturing) {
@@ -1943,8 +1942,6 @@ static Token yylex_NORMAL() {
 				if (Symbol const *sym = sym_FindExactSymbol(std::get<std::string>(token.value));
 				    sym && sym->type == SYM_EQUS) {
 					beginExpansion(sym->getEqus(), sym->name);
-					// We cannot do `MUSTTAIL return yylex_NORMAL();` because tail call optimization
-					// requires the return value to be "trivially destructible", and `Token` is not.
 					continue; // Restart, reading from the new buffer
 				}
 			}

src/link/assign.cpp

@@ -15,7 +15,6 @@
 #include "helpers.hpp"
 #include "itertools.hpp"
 #include "linkdefs.hpp"
-#include "platform.hpp" // MUSTTAIL
 #include "verbosity.hpp"
 
 #include "link/main.hpp"
@@ -119,6 +118,7 @@ static MemoryLocation getStartLocation(Section const &section) {
 static std::optional<size_t> getPlacement(Section const &section, MemoryLocation &location) {
 	SectionTypeInfo const &typeInfo = sectionTypeInfo[section.type];
 
+	for (;;) {
 		// Switch to the beginning of the next bank
 		std::deque<FreeSpace> &bankMem = memory[section.type][location.bank - typeInfo.firstBank];
 		size_t spaceIdx = 0;
@@ -137,12 +137,11 @@ static std::optional<size_t> getPlacement(Section const &section, MemoryLocation
 			// Go to the next *possible* location
 			if (section.isAddressFixed) {
 				// If the address is fixed, there can be only one candidate block per bank;
-			// if we already reached it, give up.
-			if (location.address < section.org) {
-				location.address = section.org;
-			} else {
-				break; // Try again in next bank
+				// if we already reached it, give up and try again in the next bank.
+				if (location.address >= section.org) {
+					break;
 				}
+				location.address = section.org;
 			} else if (section.isAlignFixed) {
 				// Move to next aligned location
 				// Move back to alignment boundary
@@ -204,7 +203,8 @@ static std::optional<size_t> getPlacement(Section const &section, MemoryLocation
 			return std::nullopt;
 		}
 
-	MUSTTAIL return getPlacement(section, location);
+		// Try again in the next iteration.
+	}
 }
 
 static std::string getSectionDescription(Section const &section) {