stdio.h: add std{in,out,err} macros; regex.h: add REG_MINIMAL macro

include/bits/stdio.h

@@ -9,5 +9,9 @@ typedef struct FILE FILE;
 // A typedef doesn't suffice, because libgmp uses this definition to check if
 // STDIO was loaded.
 #define FILE FILE
+// Likewise, stdin, stdout, and stderr are expected to be macros.
+#define stdin stdin
+#define stdout stdout
+#define stderr stderr
 
 #endif /* _BITS_STDIO_H */