Add logging functions

Named "vlogs" because they're logs for VVVVVV. Also it's a funny name.

desktop_version/CMakeLists.txt

@@ -112,6 +112,7 @@ set(VVV_SRC
 	src/GlitchrunnerMode.c
 	src/Network.c
 	src/ThirdPartyDeps.c
+	src/Vlogging.c
 	src/Xoshiro.c
 	../third_party/physfs/extras/physfsrwops.c
 )

desktop_version/src/Vlogging.c

@@ -0,0 +1,50 @@
+#include <stdarg.h>
+#include <stdio.h>
+
+int vlog_info(const char* text, ...)
+{
+    va_list list;
+    int retval;
+
+    printf("[INFO] ");
+
+    va_start(list, text);
+    retval = vprintf(text, list);
+    va_end(list);
+
+    putchar('\n');
+
+    return retval;
+}
+
+int vlog_warn(const char* text, ...)
+{
+    va_list list;
+    int retval;
+
+    fprintf(stderr, "[WARN] ");
+
+    va_start(list, text);
+    retval = vfprintf(stderr, text, list);
+    va_end(list);
+
+    fputc('\n', stderr);
+
+    return retval;
+}
+
+int vlog_error(const char* text, ...)
+{
+    va_list list;
+    int retval;
+
+    fprintf(stderr, "[ERROR] ");
+
+    va_start(list, text);
+    retval = vfprintf(stderr, text, list);
+    va_end(list);
+
+    fputc('\n', stderr);
+
+    return retval;
+}

desktop_version/src/Vlogging.h

@@ -0,0 +1,19 @@
+#ifndef VLOGGING_H
+#define VLOGGING_H
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+int vlog_info(const char* text, ...);
+
+int vlog_warn(const char* text, ...);
+
+int vlog_error(const char* text, ...);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* VLOGGING_H */