separate getc/putc from fgetc/fputc

for conformance, two functions should not have the same address. a
conforming program could use the addresses of getc and fgetc in ways
that assume they are distinct. normally i would just use a wrapper,
but these functions are so small and performance-critical that an
extra layer of function call could make the one that's a wrapper
nearly twice as slow, so I'm just duplicating the code instead.

src/stdio/putc.c

@@ -0,0 +1,12 @@
+#include "stdio_impl.h"
+
+int putc(int c, FILE *f)
+{
+	if (f->lock < 0 || !__lockfile(f))
+		return putc_unlocked(c, f);
+	c = putc_unlocked(c, f);
+	__unlockfile(f);
+	return c;
+}
+
+weak_alias(putc, _IO_putc);