Change how glgen.sh outputs files

This fixes building wlroots as a subproject.

glgen.sh

@@ -7,16 +7,15 @@
 # to fail if it can't load the function. You'll need to check if that function
 # is NULL before using it.
 
-if [ $# -ne 3 ]; then
+if [ $# -ne 2 ]; then
 	exit 1
 fi
 
 SPEC=$1
-OUT_C=$2
-OUT_H=$3
+OUTDIR=$2
 
 BASE=$(basename "$SPEC" .txt)
-INCLUDE_GUARD=$(printf %s "$OUT_H" | tr -c [:alnum:] _ | tr [:lower:] [:upper:])
+INCLUDE_GUARD=$(printf %s_%s_H "$OUTDIR" "$BASE" | tr -c [:alnum:] _ | tr [:lower:] [:upper:])
 
 DECL=""
 DEFN=""
@@ -56,9 +55,9 @@ while read -r COMMAND; do
 	if [ $OPTIONAL -eq 0 ]; then
 		LOADER="$LOADER$(printf "\n$CHECK_FMT" "$COMMAND" "$COMMAND")"
 	fi
-done < $SPEC
+done < "$SPEC"
 
-cat > $OUT_H << EOF
+cat > "$OUTDIR/$BASE.h" << EOF
 #ifndef $INCLUDE_GUARD
 #define $INCLUDE_GUARD
 
@@ -75,9 +74,9 @@ $DECL
 #endif
 EOF
 
-cat > $OUT_C << EOF
+cat > "$OUTDIR/$BASE.c" << EOF
 #include <wlr/util/log.h>
-#include "$OUT_H"
+#include "$BASE.h"
 $DEFN
 
 bool load_$BASE(void) {

render/meson.build

@@ -4,7 +4,7 @@ glapi = custom_target(
 	'glapi',
 	input: 'glapi.txt',
 	output: ['@BASENAME@.c', '@BASENAME@.h'],
-	command: [glgen, '@INPUT@', '@OUTPUT0@', '@OUTPUT1@'],
+	command: [glgen, '@INPUT@', '@OUTDIR@'],
 )
 
 lib_wlr_render = static_library(