Consider a different hash algorithm for the various hash maps+sets

[Rangi42]

See https://github.com/taviso/swisstable

std::unordered_map<std::string, T>:

src/asm/charmap.cpp:37:static std::unordered_map<std::string, size_t> charmapMap; // Indexes into `charmapList`
src/asm/lexer.cpp:140:static std::unordered_map<std::string, int, CaseInsensitive, CaseInsensitive> keywordDict = {
src/asm/main.cpp:136:   std::unordered_map<std::string, std::vector<StateFeature>> stateFileSpecs;
src/asm/section.cpp:44:std::unordered_map<std::string, size_t> sectionMap; // Indexes into `sectionList`
src/asm/symbol.cpp:22:std::unordered_map<std::string, Symbol> symbols;
src/link/section.cpp:14:std::unordered_map<std::string, size_t> sectionMap; // Indexes into `sectionList`
src/link/symbol.cpp:15:std::unordered_map<std::string, Symbol *> symbols;
src/link/symbol.cpp:16:std::unordered_map<std::string, std::vector<Symbol *>> localSymbols;

Other std::(unordered_)?(map|set):

src/asm/charmap.cpp:48:         std::map<size_t, std::string> mappings;
src/asm/symbol.cpp:23:std::unordered_set<std::string> purgedSymbols;
src/gfx/pal_packing.cpp:156:        std::unordered_set<uint16_t> &colors,
src/gfx/pal_packing.cpp:167:    std::unordered_set<uint16_t> &uniqueColors() const {
src/gfx/pal_packing.cpp:180:            static std::unordered_set<uint16_t> colors;
src/gfx/pal_packing.cpp:303:            std::unordered_set<uint16_t> colors;
src/gfx/process.cpp:904:        std::unordered_set<TileData> tileset;
src/gfx/process.cpp:1118:               std::unordered_set<uint16_t> tileColors;

[Rangi42]

Apparently gcc and clang already use MurmurHash3, which can process four bytes at a time (vectorized) unlike FNV-1a. And I wouldn't be replacing the entire unordered_map data structure, only its hash function.