QUIET macro not defined on non-__GNUC__ compiler

[fuhsnn]

The macro is only defined on gcc or clang:

toybox/lib/portability.h

Lines 44 to 54 in 9cde583

	#ifdef __GNUC__
	#ifndef __clang__
	#define QUIET = 0 // shut up false positive "may be used uninitialized" warning
	#else
	#define QUIET
	#endif
	#define printf_format __attribute__((format(printf, 1, 2)))
	#else
	#define printf_format
	#endif

For a compiler that doesn't define __GNUC__, it will be undefined when encountered here:

toybox/lib/net.c

Line 184 in 9cde583

char *ret QUIET, *ss QUIET;

Adding a dummy define here could be a fix.

diff --git a/lib/portability.h b/lib/portability.h
index 0b9e282..49cee36 100644
--- a/lib/portability.h
+++ b/lib/portability.h
@@ -50,6 +50,7 @@
 #endif
 #define printf_format  __attribute__((format(printf, 1, 2)))
 #else
+#define QUIET
 #define printf_format
 #endif