vendor/libc: a bunch of additions

All these additions are to allow Dear ImGui to be compiled natively.

vendor/libc/include/stdio.h

@@ -1,8 +1,14 @@
-#include <stddef.h>
-#include <stdarg.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 #pragma once
 
+#include <alloca.h>
+#include <assert.h>
+#include <stdarg.h>
+#include <stddef.h>
+
 typedef struct {} FILE;
 
 #define SEEK_SET 0
@@ -12,6 +18,8 @@ typedef struct {} FILE;
 #define stdout ((FILE *)2)
 #define stderr ((FILE *)3)
 
+#define EOF -1
+
 FILE *fopen(const char *, char *);
 int fclose(FILE *);
 int fseek(FILE *, long, int);
@@ -21,6 +29,10 @@ size_t fwrite(const void *, size_t, size_t, FILE *);
 
 int vfprintf(FILE *, const char *, va_list);
 int vsnprintf(char *, size_t, const char *, va_list);
+int vsprintf(char *, const char *, va_list);
+
+int putchar(int ch);
+int getchar();
 
 static inline int snprintf(char *buf, size_t size, const char *fmt, ...) {
 	va_list args;
@@ -30,6 +42,14 @@ static inline int snprintf(char *buf, size_t size, const char *fmt, ...) {
 	return result;
 }
 
+static inline int sprintf(char *buf, const char *fmt, ...) {
+	va_list args;
+	va_start(args, fmt);
+	int result = vsprintf(buf, fmt, args);
+	va_end(args);
+	return result;
+}
+
 static inline int fprintf(FILE *f, const char *fmt, ...) {
 	va_list args;
 	va_start(args, fmt);
@@ -45,3 +65,37 @@ static inline int printf(const char *fmt, ...) {
 	va_end(args);
 	return result;
 }
+
+int __sscanf(const char *str, const char *format, void *ptrs);
+
+static inline int vsscanf(const char *str, const char *format, va_list ap) {
+	int count = 0;
+	for (int i = 0; format[i]; i++) {
+		if (format[i] == '%') {
+			if (format[i+1] == '%') {
+				i++;
+				continue;
+			}
+			count++;
+		}
+	}
+
+	void **ptrs = (void **)(alloca(count*sizeof(void *)));
+	for (int i = 0; i < count; i++) {
+		ptrs[i] = va_arg(ap, void *);
+	}
+
+	return __sscanf(str, format, ptrs);
+}
+
+static inline int sscanf(const char *str, const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	int res = vsscanf(str, format, args);
+	va_end(args);
+	return res;
+}
+
+#ifdef __cplusplus
+}
+#endif