Add a -Wunmapped-char warning for characters not in the charmap (#1023)

Fixes #1022

src/asm/charmap.c

@@ -242,6 +242,7 @@ size_t charmap_ConvertNext(char const **input, uint8_t **output)
 				return 1;
 
 			} else if (**input) { // No match found, but there is some input left
+				int firstChar = **input;
 				// This will write the codepoint's value to `output`, little-endian
 				size_t codepointLen = readUTF8Char(output ? *output : NULL,
 								   *input);
@@ -254,6 +255,12 @@ size_t charmap_ConvertNext(char const **input, uint8_t **output)
 				if (output)
 					*output += codepointLen;
 
+				// Check if the character map is not the default "main" one, or if
+				// it has any mappings defined
+				if (strcmp(charmap->name, "main") || charmap->usedNodes > 1)
+					warning(WARNING_UNMAPPED_CHAR,
+						"Unmapped character %s\n", printChar(firstChar));
+
 				return codepointLen;
 
 			} else { // End of input

src/asm/warning.c

@@ -38,6 +38,7 @@ static const enum WarningState defaultWarnings[ARRAY_SIZE(warningStates)] = {
 	[WARNING_OBSOLETE]		= WARNING_ENABLED,
 	[WARNING_SHIFT]			= WARNING_DISABLED,
 	[WARNING_SHIFT_AMOUNT]		= WARNING_DISABLED,
+	[WARNING_UNMAPPED_CHAR]		= WARNING_ENABLED,
 	[WARNING_USER]			= WARNING_ENABLED,
 
 	[WARNING_NUMERIC_STRING_1]	= WARNING_ENABLED,
@@ -85,6 +86,7 @@ static const char * const warningFlags[NB_WARNINGS] = {
 	"obsolete",
 	"shift",
 	"shift-amount",
+	"unmapped-char",
 	"user",
 
 	// Parametric warnings
@@ -160,6 +162,7 @@ static uint8_t const _wallCommands[] = {
 	WARNING_LONG_STR,
 	WARNING_NESTED_COMMENT,
 	WARNING_OBSOLETE,
+	WARNING_UNMAPPED_CHAR,
 	WARNING_NUMERIC_STRING_1,
 	META_WARNING_DONE
 };
@@ -191,6 +194,7 @@ static uint8_t const _weverythingCommands[] = {
 	WARNING_OBSOLETE,
 	WARNING_SHIFT,
 	WARNING_SHIFT_AMOUNT,
+	WARNING_UNMAPPED_CHAR,
 	WARNING_NUMERIC_STRING_1,
 	WARNING_NUMERIC_STRING_2,
 	WARNING_TRUNCATION_1,