Use concrete types instead of auto when convenient and not redundant (#1757)

include/gfx/main.hpp

@@ -110,7 +110,7 @@ struct Palette {
 };
 
 // Flipping tends to happen fairly often, so take a bite out of dcache to speed it up
-static constexpr auto flipTable = ([]() constexpr {
+static std::array<uint16_t, 256> flipTable = ([]() constexpr {
 	std::array<uint16_t, 256> table{};
 	for (uint16_t i = 0; i < table.size(); i++) {
 		// To flip all the bits, we'll flip both nibbles, then each nibble half, etc.

include/gfx/rgba.hpp

@@ -33,7 +33,9 @@ struct Rgba {
 	// Returns this RGBA as a 32-bit number that can be printed in hex (`%08x`) to yield its CSS
 	// representation
 	uint32_t toCSS() const {
-		auto shl = [](uint8_t val, unsigned shift) { return static_cast<uint32_t>(val) << shift; };
+		constexpr auto shl = [](uint8_t val, unsigned shift) {
+			return static_cast<uint32_t>(val) << shift;
+		};
 		return shl(red, 24) | shl(green, 16) | shl(blue, 8) | shl(alpha, 0);
 	}