Use std::unordered_map and std::vector for sections

This allows us to control the order in which sections are iterated,
instead of it depending on the internals of `std::map`. (This order
is arbitrary, but should be deterministic regardless.)

src/link/section.cpp

@@ -3,18 +3,20 @@
 #include "link/section.hpp"
 
 #include <assert.h>
+#include <deque>
 #include <inttypes.h>
-#include <map>
 #include <stdlib.h>
 #include <string.h>
+#include <unordered_map>
 
 #include "error.hpp"
 
-std::map<std::string, std::unique_ptr<Section>> sections;
+std::vector<std::unique_ptr<Section>> sectionList;
+std::unordered_map<std::string, size_t> sectionMap; // Indexes into `sectionList`
 
 void sect_ForEach(void (*callback)(Section &)) {
-	for (auto &it : sections)
-		callback(*it.second);
+	for (auto it = sectionList.rbegin(); it != sectionList.rend(); it++)
+		callback(*it->get());
 }
 
 static void checkSectUnionCompat(Section &target, Section &other) {
@@ -215,13 +217,14 @@ void sect_AddSection(std::unique_ptr<Section> &&section) {
 		);
 	} else {
 		// If not, add it
-		sections.emplace(section->name, std::move(section));
+		sectionMap.emplace(section->name, sectionList.size());
+		sectionList.push_back(std::move(section));
 	}
 }
 
 Section *sect_GetSection(std::string const &name) {
-	auto search = sections.find(name);
-	return search != sections.end() ? search->second.get() : nullptr;
+	auto search = sectionMap.find(name);
+	return search != sectionMap.end() ? sectionList[search->second].get() : nullptr;
 }
 
 static void doSanityChecks(Section &section) {

test/asm/charmap-inheritance.asm

@@ -13,7 +13,7 @@ SECTION "test", ROM0
 	charmap "<FAR>",    $08
 
 	; At this point, enough nodes were allocated for 'foo' to be reallocated.
-	; Its value in the charmaps' std::map should have been updated too,
+	; Its value in the charmaps' `std::unordered_map` should have been updated too,
 	; so that usages of 'foo' will not segfault.
 
 	; This uses 'foo; by switching to it.

test/asm/sym-collision.asm

@@ -2,7 +2,7 @@ SECTION "Collision course", OAM[$FE00]
 
 ; All the following symbols used to collide with our custom hashmap,
 ; which at some point caused `PURGE` to malfunction with them.
-; We now use C++ `std::map` which reliably handles collisions.
+; We now use C++ `std::unordered_map` which reliably handles collisions.
 aqfj: ds 1 ; Give them different addresses
 cxje: ds 1
 dgsd: ds 1