Report attempts to assign a SDCC area in a way inconsistent with its data

This actually avoids breaking the (segfaulting) invariant that
a section whose type "has data" has as many bytes of `->data` as
its `->size`.

src/link/script.y

@@ -594,10 +594,29 @@ static void placeSection(std::string const &name, bool isOptional) {
 	assume(section->offset == 0);
 	// Check that the linker script doesn't contradict what the code says.
 	if (section->type == SECTTYPE_INVALID) {
+		// A section that has data must get assigned a type that requires data.
+		if (!sect_HasData(activeType) && !section->data.empty()) {
+			scriptError(
+			    context,
+			    "\"%s\" is specified to be a %s section, but it contains data",
+			    name.c_str(),
+			    typeInfo.name.c_str()
+			);
+		} else if (sect_HasData(activeType) && section->data.empty() && section->size != 0) {
+			// A section that lacks data can only be assigned to a type that requires data
+			// if it's empty.
+			scriptError(
+			    context,
+			    "\"%s\" is specified to be a %s section, but it doesn't contain data",
+			    name.c_str(),
+			    typeInfo.name.c_str()
+			);
+		} else {
 			// SDCC areas don't have a type assigned yet, so the linker script is used to give them one.
 			for (Section *fragment = section; fragment; fragment = fragment->nextu.get()) {
 				fragment->type = activeType;
 			}
+		}
 	} else if (section->type != activeType) {
 		scriptError(
 		    context,