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stdio, ape/stdio: fix order of operations in putc

When calling putc, we need to return either EOF
or the character returned. To distinguish the
two, we need to avoid sign extending 0xff. The
code attempted to do this, but the order of
operations was wrong, so we ended up masking,
setting a character, and then sign extending
the character.

This fixes things so we mask after assignment.

--- a/sys/include/ape/stdio.h

+++ b/sys/include/ape/stdio.h

@@ -106,7 +106,7 @@

 #define	getchar()	getc(stdin)

 extern char *gets(char *);

 extern int putc(int, FILE *);

-#define	putc(c, f) ((f)->wp>=(f)->rp?_IO_putc(c, f):(*(f)->wp++=(c)&_IO_CHMASK))

+#define	putc(c, f) ((f)->wp>=(f)->rp?_IO_putc(c, f):((*(f)->wp++=(c))&_IO_CHMASK))

 extern int _IO_putc(int, FILE *);

 extern int putchar(int);

 #define	putchar(c)	putc(c, stdout)

--- a/sys/include/stdio.h

+++ b/sys/include/stdio.h

@@ -92,7 +92,7 @@

 #define	getchar()	getc(stdin)

 char *gets(char *);

 int putc(int, FILE *);

-#define	putc(c, f) ((f)->wp>=(f)->rp?_IO_putc(c, f):(*(f)->wp++=(c)&_IO_CHMASK))

+#define	putc(c, f) ((f)->wp>=(f)->rp?_IO_putc(c, f):((*(f)->wp++=(c))&_IO_CHMASK))

 int _IO_putc(int, FILE *);

 int putchar(int);

 #define	putchar(c)	putc(c, stdout)

-- 

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